PAPI: Cache connected client instances

Disconnect+connect cycle is expensive and slow.
This change tracks connected client instances
so later "connect" to the same target uses it.

Explicit disconnects are allowed (and executed before VPP ends),
but once again disconnected instances are cached and reused,
as creating a new instance is more expensive than just connect.

+ Add missing checks on interfaces being up to appropriate keyword.
 + Use appropriate keywords.
 + Add a comment explaining why a simpler keyword is not appropriate.
+ Improve VPP checks in containers.
 + Fix the vppctl check to actually work.
 + Add PAPI check to ensure VPP is really ready.
 + Delay/reorder checks to make them faster with multiple containers.
 + Leave some TODOs to improve various lifecycles later.
+ As we do not stop VPP in test/suite teardown:
 + One final disconnect is needed, added to __init__.robot teardowns.
 - Import of the final disconnect keyword is ugly, but it works.
- We could use a hashable class for distinguishing node+socket pairs.
- Are we connecting to VPP inside VMs?

Change-Id: I49cd726740c3e8cae1591c7c84b85a447241228f
Signed-off-by: Vratko Polak <vrpolak@cisco.com>

4 files changed, 476 insertions, 97 deletions

diff --git a/resources/libraries/python/ContainerUtils.py b/resources/libraries/python/ContainerUtils.py
index 59d98aa538..3d70684695 100644
--- a/resources/libraries/python/ContainerUtils.py
+++ b/resources/libraries/python/ContainerUtils.py
@@ -23,9 +23,11 @@ from robot.libraries.BuiltIn import BuiltIn
 
 from resources.libraries.python.Constants import Constants
 from resources.libraries.python.CpuUtils import CpuUtils
+from resources.libraries.python.PapiExecutor import PapiSocketExecutor
 from resources.libraries.python.ssh import SSH
 from resources.libraries.python.topology import Topology, SocketType
 from resources.libraries.python.VppConfigGenerator import VppConfigGenerator
+from resources.libraries.python.VPPUtil import VPPUtil
 
 
 __all__ = [
@@ -141,23 +143,52 @@ class ContainerManager:
             self.engine.container = self.containers[container]
             self.engine.execute(command)
 
-    def start_vpp_in_all_containers(self):
+    def start_vpp_in_all_containers(self, verify=True):
         """Start VPP in all containers."""
         for container in self.containers:
             self.engine.container = self.containers[container]
-            self.engine.start_vpp()
+            # For multiple containers, delayed verify is faster.
+            self.engine.start_vpp(verify=False)
+        if verify:
+            self.verify_vpp_in_all_containers()
 
-    def restart_vpp_in_all_containers(self):
+    def _disconnect_papi_to_all_containers(self):
+        """Disconnect any open PAPI connections to VPPs in containers.
+
+        The current PAPI implementation caches open connections,
+        so explicit disconnect is needed before VPP becomes inaccessible.
+
+        Currently this is a protected method, as restart, stop and destroy
+        are the only dangerous methods, and all are handled by ContainerManager.
+        """
+        for container_object in self.containers.values():
+            PapiSocketExecutor.disconnect_by_node_and_socket(
+                container_object.node,
+                container_object.api_socket,
+            )
+
+    def restart_vpp_in_all_containers(self, verify=True):
         """Restart VPP in all containers."""
+        self._disconnect_papi_to_all_containers()
         for container in self.containers:
             self.engine.container = self.containers[container]
-            self.engine.restart_vpp()
+            # For multiple containers, delayed verify is faster.
+            self.engine.restart_vpp(verify=False)
+        if verify:
+            self.verify_vpp_in_all_containers()
 
     def verify_vpp_in_all_containers(self):
         """Verify that VPP is installed and running in all containers."""
+        # For multiple containers, multiple fors are faster.
+        for container in self.containers:
+            self.engine.container = self.containers[container]
+            self.engine.verify_vppctl()
         for container in self.containers:
             self.engine.container = self.containers[container]
-            self.engine.verify_vpp()
+            self.engine.adjust_privileges()
+        for container in self.containers:
+            self.engine.container = self.containers[container]
+            self.engine.verify_vpp_papi()
 
     def configure_vpp_in_all_containers(self, chain_topology, **kwargs):
         """Configure VPP in all containers.
@@ -481,12 +512,16 @@ class ContainerManager:
 
     def stop_all_containers(self):
         """Stop all containers."""
+        # TODO: Rework if containers can be affected outside ContainerManager.
+        self._disconnect_papi_to_all_containers()
         for container in self.containers:
             self.engine.container = self.containers[container]
             self.engine.stop()
 
     def destroy_all_containers(self):
         """Destroy all containers."""
+        # TODO: Rework if containers can be affected outside ContainerManager.
+        self._disconnect_papi_to_all_containers()
         for container in self.containers:
             self.engine.container = self.containers[container]
             self.engine.destroy()
@@ -543,7 +578,7 @@ class ContainerEngine:
         """System info."""
         raise NotImplementedError
 
-    def start_vpp(self):
+    def start_vpp(self, verify=True):
         """Start VPP inside a container."""
         self.execute(
             u"setsid /usr/bin/vpp -c /etc/vpp/startup.conf "
@@ -556,38 +591,51 @@ class ContainerEngine:
             self.container.node,
             SocketType.PAPI,
             self.container.name,
-            f"/tmp/vpp_sockets/{self.container.name}/api.sock"
+            self.container.api_socket,
         )
         topo_instance.add_new_socket(
             self.container.node,
             SocketType.STATS,
             self.container.name,
-            f"/tmp/vpp_sockets/{self.container.name}/stats.sock"
+            self.container.stats_socket,
         )
-        self.verify_vpp()
-        self.adjust_privileges()
+        if verify:
+            self.verify_vpp()
 
-    def restart_vpp(self):
+    def restart_vpp(self, verify=True):
         """Restart VPP service inside a container."""
         self.execute(u"pkill vpp")
-        self.start_vpp()
+        self.start_vpp(verify=verify)
+
+    def verify_vpp(self):
+        """Verify VPP is running and ready."""
+        self.verify_vppctl()
+        self.adjust_privileges()
+        self.verify_vpp_papi()
 
     # TODO Rewrite to use the VPPUtil.py functionality and remove this.
-    def verify_vpp(self, retries=120, retry_wait=1):
+    def verify_vppctl(self, retries=120, retry_wait=1):
         """Verify that VPP is installed and running inside container.
 
+        This function waits a while so VPP can start.
+        PCI interfaces are listed for debug purposes.
+        When the check passes, VPP API socket is created on remote side,
+        but perhaps its directory does not have the correct access rights yet.
+
         :param retries: Check for VPP for this number of times Default: 120
         :param retry_wait: Wait for this number of seconds between retries.
         """
         for _ in range(retries + 1):
             try:
+                # Execute puts the command into single quotes,
+                # so inner arguments are enclosed in qouble quotes here.
                 self.execute(
-                    u"vppctl show pci 2>&1 | "
-                    u"fgrep -v 'Connection refused' | "
-                    u"fgrep -v 'No such file or directory'"
+                    u'vppctl show pci 2>&1 | '
+                    u'fgrep -v "Connection refused" | '
+                    u'fgrep -v "No such file or directory"'
                 )
                 break
-            except RuntimeError:
+            except (RuntimeError, AssertionError):
                 sleep(retry_wait)
         else:
             self.execute(u"cat /tmp/vppd.log")
@@ -599,6 +647,32 @@ class ContainerEngine:
         """Adjust privileges to control VPP without sudo."""
         self.execute("chmod -R o+rwx /run/vpp")
 
+    def verify_vpp_papi(self, retries=120, retry_wait=1):
+        """Verify that VPP is available for PAPI.
+
+        This also opens and caches PAPI connection for quick reuse.
+        The connection is disconnected when ContainerManager decides to do so.
+
+        :param retries: Check for VPP for this number of times Default: 120
+        :param retry_wait: Wait for this number of seconds between retries.
+        """
+        # Wait for success.
+        for _ in range(retries + 1):
+            try:
+                VPPUtil.vpp_show_version(
+                    node=self.container.node,
+                    remote_vpp_socket=self.container.api_socket,
+                    log=False,
+                )
+                break
+            except (RuntimeError, AssertionError):
+                sleep(retry_wait)
+        else:
+            self.execute(u"cat /tmp/vppd.log")
+            raise RuntimeError(
+                f"VPP PAPI fails in container: {self.container.name}"
+            )
+
     def create_base_vpp_startup_config(self, cpuset_cpus=None):
         """Create base startup configuration of VPP on container.
 
@@ -1188,8 +1262,18 @@ class Container:
         except KeyError:
             # Creating new attribute
             if attr == u"node":
+                # Create and cache a connected SSH instance.
                 self.__dict__[u"ssh"] = SSH()
                 self.__dict__[u"ssh"].connect(value)
+            elif attr == u"name":
+                # Socket paths to not have mutable state,
+                # this just saves some horizontal space in callers.
+                # TODO: Rename the dir so other apps can add sockets easily.
+                # E.g. f"/tmp/app_sockets/{value}/vpp_api.sock"
+                path = f"/tmp/vpp_sockets/{value}"
+                self.__dict__[u"socket_dir"] = path
+                self.__dict__[u"api_socket"] = f"{path}/api.sock"
+                self.__dict__[u"stats_socket"] = f"{path}/stats.sock"
             self.__dict__[attr] = value
         else:
             # Updating attribute base of type
diff --git a/resources/libraries/python/PapiExecutor.py b/resources/libraries/python/PapiExecutor.py
index 46fe5d583b..6b21680526 100644
--- a/resources/libraries/python/PapiExecutor.py
+++ b/resources/libraries/python/PapiExecutor.py
@@ -37,7 +37,11 @@ from resources.libraries.python.topology import Topology, SocketType
 from resources.libraries.python.VppApiCrc import VppApiCrcChecker
 
 
-__all__ = [u"PapiExecutor", u"PapiSocketExecutor"]
+__all__ = [
+    u"PapiExecutor",
+    u"PapiSocketExecutor",
+    u"Disconnector",
+]
 
 
 def dictize(obj):
@@ -73,14 +77,33 @@ def dictize(obj):
 class PapiSocketExecutor:
     """Methods for executing VPP Python API commands on forwarded socket.
 
-    The current implementation connects for the duration of resource manager.
-    Delay for accepting connection is 10s, and disconnect is explicit.
+    Previously, we used an implementation with single client instance
+    and connection being handled by a resource manager.
+    On "with" statement, the instance connected, and disconnected
+    on exit from the "with" block.
+    This was limiting (no nested with blocks) and mainly it was slow:
+    0.7 seconds per disconnect cycle on Skylake, more than 3 second on Taishan.
+
+    The currently used implementation caches the connected client instances,
+    providing speedup and making "with" blocks unnecessary.
+    But with many call sites, "with" blocks are still the main usage pattern.
+    Documentation still lists that as the intended pattern.
+
+    As a downside, clients need to be explicitly told to disconnect
+    before VPP restart.
+    There is some amount of retries and disconnects on disconnect
+    (so unresponsive VPPs do not breach test much more than needed),
+    but it is hard to verify all that works correctly.
+    Especially, if Robot crashes, files and ssh processes may leak.
+
+    Delay for accepting socket connection is 10s.
     TODO: Decrease 10s to value that is long enough for creating connection
     and short enough to not affect performance.
 
     The current implementation downloads and parses .api.json files only once
-    and stores a VPPApiClient instance (disconnected) as a class variable.
-    Accessing multiple nodes with different APIs is therefore not supported.
+    and caches client instances for reuse.
+    Cleanup metadata is added as additional attributes
+    directly to client instances.
 
     The current implementation seems to run into read error occasionally.
     Not sure if the error is in Python code on Robot side, ssh forwarding,
@@ -129,10 +152,25 @@ class PapiSocketExecutor:
     """
 
     # Class cache for reuse between instances.
-    vpp_instance = None
-    """Takes long time to create, stores all PAPI functions and types."""
+    api_root_dir = None
+    """We copy .api json files and PAPI code from DUT to robot machine.
+    This class variable holds temporary directory once created.
+    When python exits, the directory is deleted, so no downloaded file leaks.
+    The value will be set to TemporaryDirectory class instance (not string path)
+    to ensure deletion at exit."""
+    api_json_path = None
+    """String path to .api.json files, a directory somewhere in api_root_dir."""
+    api_package_path = None
+    """String path to PAPI code, a different directory under api_root_dir."""
     crc_checker = None
-    """Accesses .api.json files at creation, caching allows deleting them."""
+    """Accesses .api.json files at creation, caching speeds up accessing it."""
+    reusable_vpp_client_list = list()
+    """Each connection needs a separate client instance,
+    and each client instance creation needs to parse all .api files,
+    which takes time. If a client instance disconnects, it is put here,
+    so on next connect we can reuse intead of creating new."""
+    conn_cache = dict()
+    """Mapping from node key to connected client instance."""
 
     def __init__(self, node, remote_vpp_socket=Constants.SOCKSVR_PATH):
         """Store the given arguments, declare managed variables.
@@ -146,89 +184,214 @@ class PapiSocketExecutor:
         self._remote_vpp_socket = remote_vpp_socket
         # The list of PAPI commands to be executed on the node.
         self._api_command_list = list()
-        # The following values are set on enter, reset on exit.
-        self._temp_dir = None
-        self._ssh_control_socket = None
-        self._local_vpp_socket = None
-        self.initialize_vpp_instance()
 
-    def initialize_vpp_instance(self):
-        """Create VPP instance with bindings to API calls, store as class field.
+    def ensure_api_dirs(self):
+        """Copy files from DUT to local temporary directory.
 
-        No-op if the instance had been stored already.
+        If the directory is still there, do not copy again.
+        If copying, also initialize CRC checker (this also performs
+        static checks), and remember PAPI package path.
+        Do not add that to PATH yet.
+        """
+        cls = self.__class__
+        if cls.api_package_path:
+            return
+        cls.api_root_dir = tempfile.TemporaryDirectory(dir=u"/tmp")
+        root_path = cls.api_root_dir.name
+        # Pack, copy and unpack Python part of VPP installation from _node.
+        # TODO: Use rsync or recursive version of ssh.scp_node instead?
+        node = self._node
+        exec_cmd_no_error(node, [u"rm", u"-rf", u"/tmp/papi.txz"])
+        # Papi python version depends on OS (and time).
+        # Python 2.7 or 3.4, site-packages or dist-packages.
+        installed_papi_glob = u"/usr/lib/python3*/*-packages/vpp_papi"
+        # We need to wrap this command in bash, in order to expand globs,
+        # and as ssh does join, the inner command has to be quoted.
+        inner_cmd = u" ".join([
+            u"tar", u"cJf", u"/tmp/papi.txz", u"--exclude=*.pyc",
+            installed_papi_glob, u"/usr/share/vpp/api"
+        ])
+        exec_cmd_no_error(node, [u"bash", u"-c", u"'" + inner_cmd + u"'"])
+        scp_node(node, root_path + u"/papi.txz", u"/tmp/papi.txz", get=True)
+        run([u"tar", u"xf", root_path + u"/papi.txz", u"-C", root_path])
+        cls.api_json_path = root_path + u"/usr/share/vpp/api"
+        # Perform initial checks before .api.json files are gone,
+        # by creating the checker instance.
+        cls.crc_checker = VppApiCrcChecker(cls.api_json_path)
+        # When present locally, we finally can find the installation path.
+        cls.api_package_path = glob.glob(root_path + installed_papi_glob)[0]
+        # Package path has to be one level above the vpp_papi directory.
+        cls.api_package_path = cls.api_package_path.rsplit(u"/", 1)[0]
+
+    def ensure_vpp_instance(self):
+        """Create or reuse a closed client instance, return it.
 
         The instance is initialized for unix domain socket access,
-        it has initialized all the bindings, but it is not connected
+        it has initialized all the bindings, it is removed from the internal
+        list of disconnected instances, but it is not connected
         (to a local socket) yet.
 
-        This method downloads .api.json files from self._node
-        into a temporary directory, deletes them finally.
+        :returns: VPP client instance ready for connect.
+        :rtype: vpp_papi.VPPApiClient
         """
-        if self.vpp_instance:
-            return
-        cls = self.__class__  # Shorthand for setting class fields.
-        package_path = None
-        tmp_dir = tempfile.mkdtemp(dir=u"/tmp")
+        self.ensure_api_dirs()
+        cls = self.__class__
+        if cls.reusable_vpp_client_list:
+            # Reuse in LIFO fashion.
+            *cls.reusable_vpp_client_list, ret = cls.reusable_vpp_client_list
+            return ret
+        # Creating an instance leads to dynamic imports from VPP PAPI code,
+        # so the package directory has to be present until the instance.
+        # But it is simpler to keep the package dir around.
         try:
-            # Pack, copy and unpack Python part of VPP installation from _node.
-            # TODO: Use rsync or recursive version of ssh.scp_node instead?
-            node = self._node
-            exec_cmd_no_error(node, [u"rm", u"-rf", u"/tmp/papi.txz"])
-            # Papi python version depends on OS (and time).
-            # Python 2.7 or 3.4, site-packages or dist-packages.
-            installed_papi_glob = u"/usr/lib/python3*/*-packages/vpp_papi"
-            # We need to wrap this command in bash, in order to expand globs,
-            # and as ssh does join, the inner command has to be quoted.
-            inner_cmd = u" ".join([
-                u"tar", u"cJf", u"/tmp/papi.txz", u"--exclude=*.pyc",
-                installed_papi_glob, u"/usr/share/vpp/api"
-            ])
-            exec_cmd_no_error(node, [u"bash", u"-c", u"'" + inner_cmd + u"'"])
-            scp_node(node, tmp_dir + u"/papi.txz", u"/tmp/papi.txz", get=True)
-            run([u"tar", u"xf", tmp_dir + u"/papi.txz", u"-C", tmp_dir])
-            api_json_directory = tmp_dir + u"/usr/share/vpp/api"
-            # Perform initial checks before .api.json files are gone,
-            # by creating the checker instance.
-            cls.crc_checker = VppApiCrcChecker(api_json_directory)
-            # When present locally, we finally can find the installation path.
-            package_path = glob.glob(tmp_dir + installed_papi_glob)[0]
-            # Package path has to be one level above the vpp_papi directory.
-            package_path = package_path.rsplit(u"/", 1)[0]
-            sys.path.append(package_path)
+            sys.path.append(cls.api_package_path)
             # TODO: Pylint says import-outside-toplevel and import-error.
             # It is right, we should refactor the code and move initialization
             # of package outside.
             from vpp_papi.vpp_papi import VPPApiClient as vpp_class
-            vpp_class.apidir = api_json_directory
+            vpp_class.apidir = cls.api_json_path
             # We need to create instance before removing from sys.path.
-            cls.vpp_instance = vpp_class(
+            vpp_instance = vpp_class(
                 use_socket=True, server_address=u"TBD", async_thread=False,
-                read_timeout=14, logger=FilteredLogger(logger, u"INFO"))
+                read_timeout=14, logger=FilteredLogger(logger, u"INFO")
+            )
             # Cannot use loglevel parameter, robot.api.logger lacks support.
             # TODO: Stop overriding read_timeout when VPP-1722 is fixed.
         finally:
-            shutil.rmtree(tmp_dir)
-            if sys.path[-1] == package_path:
+            if sys.path[-1] == cls.api_package_path:
                 sys.path.pop()
+        return vpp_instance
+
+    @classmethod
+    def key_for_node_and_socket(cls, node, remote_socket):
+        """Return a hashable object to distinguish nodes.
+
+        The usual node object (of "dict" type) is not hashable,
+        and can contain mutable information (mostly virtual interfaces).
+        Use this method to get an object suitable for being a key in dict.
+
+        The fields to include are chosen by what ssh needs.
+
+        This class method is needed, for disconnect.
+
+        :param node: The node object to distinguish.
+        :param remote_socket: Path to remote socket.
+        :type node: dict
+        :type remote_socket: str
+        :return: Tuple of values distinguishing this node from similar ones.
+        :rtype: tuple of str
+        """
+        return (
+            node[u"host"],
+            node[u"port"],
+            remote_socket,
+            # TODO: Do we support sockets paths such as "~/vpp/api.socket"?
+            # If yes, add also:
+            # node[u"username"],
+        )
+
+    def key_for_self(self):
+        """Return a hashable object to distinguish nodes.
+
+        Just a wrapper around key_for_node_and_socket
+        which sets up proper arguments.
+
+        :return: Tuple of values distinguishing this node from similar ones.
+        :rtype: tuple of str
+        """
+        return self.__class__.key_for_node_and_socket(
+            self._node, self._remote_vpp_socket,
+        )
+
+    def set_connected_client(self, client):
+        """Add a connected client instance into cache.
+
+        This hides details of what the node key is.
+
+        If there already is a client for the computed key,
+        fail, as it is a sign of resource leakage.
+
+        :param client: VPP client instance in connected state.
+        :type client: vpp_papi.VPPApiClient
+        :raises RuntimeError: If related key already has a cached client.
+        """
+        key = self.key_for_self()
+        cache = self.__class__.conn_cache
+        if key in cache:
+            raise RuntimeError(f"Caching client with existing key: {key}")
+        cache[key] = client
+
+    def get_connected_client(self, check_connected=True):
+        """Return None or cached connected client.
+
+        If check_connected, RuntimeError is raised when the client is
+        not in cache. None is returned if client is not in cache
+        (and the check is disabled).
+
+        This hides details of what the node key is.
+
+        :param check_connected: Whether cache miss raises.
+        :type check_connected: bool
+        :returns: Connected client instance, or None if uncached and no check.
+        :rtype: Optional[vpp_papi.VPPApiClient]
+        :raises RuntimeError: If cache miss and check enabled.
+        """
+        key = self.key_for_self()
+        ret = self.__class__.conn_cache.get(key, None)
+
+        if ret is None:
+            if check_connected:
+                raise RuntimeError(f"Client not cached for key: {key}")
+        else:
+            # When reading logs, it is good to see which VPP is accessed.
+            logger.debug(f"Activated cached PAPI client for key: {key}")
+        return ret
 
     def __enter__(self):
         """Create a tunnel, connect VPP instance.
 
+        If the connected client is in cache, return it.
+        Only if not, create a new (or reuse a disconnected) client instance.
+
         Only at this point a local socket names are created
-        in a temporary directory, because VIRL runs 3 pybots at once,
-        so harcoding local filenames does not work.
+        in a temporary directory, as CSIT can connect to multiple VPPs.
+
+        The following attributes are added to the client instance
+        to simplify caching and cleanup:
+        csit_temp_dir
+            - Temporary socket files are created here.
+        csit_control_socket
+            - This socket controls the local ssh process doing the forwarding.
+        csit_local_vpp_socket
+            - This is the forwarded socket to talk with remote VPP.
+
+        The attribute names do not start with underscore,
+        so pylint does not complain about accessing private attribute.
+        The attribute names start with csit_ to avoid naming conflicts
+        with "real" attributes from VPP Python code.
 
         :returns: self
         :rtype: PapiSocketExecutor
         """
+        # Do we have the connected instance in the cache?
+        vpp_instance = self.get_connected_client(check_connected=False)
+        if vpp_instance is not None:
+            return self
+        # No luck, create and connect a new instance.
         time_enter = time.time()
-        # Parsing takes longer than connecting, prepare instance before tunnel.
-        vpp_instance = self.vpp_instance
         node = self._node
-        self._temp_dir = tempfile.mkdtemp(dir=u"/tmp")
-        self._local_vpp_socket = self._temp_dir + u"/vpp-api.sock"
-        self._ssh_control_socket = self._temp_dir + u"/ssh.sock"
-        ssh_socket = self._ssh_control_socket
+        # Parsing takes longer than connecting, prepare instance before tunnel.
+        vpp_instance = self.ensure_vpp_instance()
+        # Store into cache as soon as possible.
+        # If connection fails, it is better to attempt disconnect anyway.
+        self.set_connected_client(vpp_instance)
+        # Set additional attributes.
+        vpp_instance.csit_temp_dir = tempfile.TemporaryDirectory(dir=u"/tmp")
+        temp_path = vpp_instance.csit_temp_dir.name
+        api_socket = temp_path + u"/vpp-api.sock"
+        vpp_instance.csit_local_vpp_socket = api_socket
+        ssh_socket = temp_path + u"/ssh.sock"
+        vpp_instance.csit_control_socket = ssh_socket
         # Cleanup possibilities.
         ret_code, _ = run([u"ls", ssh_socket], check=False)
         if ret_code != 2:
@@ -243,19 +406,21 @@ class PapiSocketExecutor:
             run([u"rm", u"-vrf", ssh_socket])
         # Even if ssh can perhaps reuse this file,
         # we need to remove it for readiness detection to work correctly.
-        run([u"rm", u"-rvf", self._local_vpp_socket])
+        run([u"rm", u"-rvf", api_socket])
         # We use sleep command. The ssh command will exit in 30 second,
         # unless a local socket connection is established,
         # in which case the ssh command will exit only when
         # the ssh connection is closed again (via control socket).
         # The log level is to suppress "Warning: Permanently added" messages.
         ssh_cmd = [
-            u"ssh", u"-S", ssh_socket, u"-M",
-            u"-o", u"LogLevel=ERROR", u"-o", u"UserKnownHostsFile=/dev/null",
+            u"ssh", u"-S", ssh_socket, u"-M", u"-L",
+            api_socket + u":" + self._remote_vpp_socket,
+            u"-p", str(node[u"port"]),
+            u"-o", u"LogLevel=ERROR",
+            u"-o", u"UserKnownHostsFile=/dev/null",
             u"-o", u"StrictHostKeyChecking=no",
             u"-o", u"ExitOnForwardFailure=yes",
-            u"-L", self._local_vpp_socket + u":" + self._remote_vpp_socket,
-            u"-p", str(node[u"port"]), node[u"username"] + u"@" + node[u"host"],
+            node[u"username"] + u"@" + node[u"host"],
             u"sleep", u"30"
         ]
         priv_key = node.get(u"priv_key")
@@ -282,7 +447,7 @@ class PapiSocketExecutor:
         while time.time() < time_stop:
             # It can take a moment for ssh to create the socket file.
             ret_code, _ = run(
-                [u"ls", u"-l", self._local_vpp_socket], check=False
+                [u"ls", u"-l", api_socket], check=False
             )
             if not ret_code:
                 break
@@ -293,7 +458,7 @@ class PapiSocketExecutor:
             # Socket up means the key has been read. Delete file by closing it.
             key_file.close()
         # Everything is ready, set the local socket address and connect.
-        vpp_instance.transport.server_address = self._local_vpp_socket
+        vpp_instance.transport.server_address = api_socket
         # It seems we can get read error even if every preceding check passed.
         # Single retry seems to help.
         for _ in range(2):
@@ -312,16 +477,100 @@ class PapiSocketExecutor:
         return self
 
     def __exit__(self, exc_type, exc_val, exc_tb):
-        """Disconnect the vpp instance, tear down the SHH tunnel.
+        """No-op, the client instance remains in cache in connected state."""
+
+    @classmethod
+    def disconnect_by_key(cls, key):
+        """Disconnect a connected client instance, noop it not connected.
 
         Also remove the local sockets by deleting the temporary directory.
-        Arguments related to possible exception are entirely ignored.
+        Put disconnected client instances to the reuse list.
+        The added attributes are not cleaned up,
+        as their values will get overwritten on next connect.
+
+        This method is useful for disconnect_all type of work.
+
+        :param key: Tuple identifying the node (and socket).
+        :type key: tuple of str
         """
-        self.vpp_instance.disconnect()
+        client_instance = cls.conn_cache.get(key, None)
+        if client_instance is None:
+            return
+        logger.debug(f"Disconnecting by key: {key}")
+        client_instance.disconnect()
         run([
-            u"ssh", u"-S", self._ssh_control_socket, u"-O", u"exit", u"0.0.0.0"
+            u"ssh", u"-S", client_instance.csit_control_socket, u"-O",
+            u"exit", u"0.0.0.0"
         ], check=False)
-        shutil.rmtree(self._temp_dir)
+        # Temp dir has autoclean, but deleting explicitly
+        # as an error can happen.
+        try:
+            client_instance.csit_temp_dir.cleanup()
+        except FileNotFoundError:
+            # There is a race condition with ssh removing its ssh.sock file.
+            # Single retry should be enough to ensure the complete removal.
+            shutil.rmtree(client_instance.csit_temp_dir.name)
+        # Finally, put disconnected clients to reuse list.
+        cls.reusable_vpp_client_list.append(client_instance)
+        # Invalidate cache last. Repeated errors are better than silent leaks.
+        del cls.conn_cache[key]
+
+    @classmethod
+    def disconnect_by_node_and_socket(
+            cls, node, remote_socket=Constants.SOCKSVR_PATH
+        ):
+        """Disconnect a connected client instance, noop it not connected.
+
+        Also remove the local sockets by deleting the temporary directory.
+        Put disconnected client instances to the reuse list.
+        The added attributes are not cleaned up,
+        as their values will get overwritten on next connect.
+
+        Call this method just before killing/restarting remote VPP instance.
+        """
+        key = cls.key_for_node_and_socket(node, remote_socket)
+        return cls.disconnect_by_key(key)
+
+    @classmethod
+    def disconnect_all_sockets_by_node(cls, node):
+        """Disconnect all socket connected client instance.
+
+        Noop if not connected.
+
+        Also remove the local sockets by deleting the temporary directory.
+        Put disconnected client instances to the reuse list.
+        The added attributes are not cleaned up,
+        as their values will get overwritten on next connect.
+
+        Call this method just before killing/restarting remote VPP instance.
+        """
+        sockets = Topology.get_node_sockets(node, socket_type=SocketType.PAPI)
+        if sockets:
+            for socket in sockets.values():
+                # TODO: Remove sockets from topology.
+                PapiSocketExecutor.disconnect_by_node_and_socket(node, socket)
+        # Always attempt to disconnect the default socket.
+        return cls.disconnect_by_node_and_socket(node)
+
+    @staticmethod
+    def disconnect_all_papi_connections():
+        """Disconnect all connected client instances, tear down the SSH tunnels.
+
+        Also remove the local sockets by deleting the temporary directory.
+        Put disconnected client instances to the reuse list.
+        The added attributes are not cleaned up,
+        as their values will get overwritten on next connect.
+
+        This should be a class method,
+        but we prefer to call static methods from Robot.
+
+        Call this method just before killing/restarting all VPP instances.
+        """
+        cls = PapiSocketExecutor
+        # Iterate over copy of entries so deletions do not mess with iterator.
+        keys_copy = list(cls.conn_cache.keys())
+        for key in keys_copy:
+            cls.disconnect_by_key(key)
 
     def add(self, csit_papi_command, history=True, **kwargs):
         """Add next command to internal command list; return self.
@@ -517,7 +766,7 @@ class PapiSocketExecutor:
         :rtype: list of dict
         :raises RuntimeError: If the replies are not all correct.
         """
-        vpp_instance = self.vpp_instance
+        vpp_instance = self.get_connected_client()
         local_list = self._api_command_list
         # Clear first as execution may fail.
         self._api_command_list = list()
@@ -531,10 +780,10 @@ class PapiSocketExecutor:
                 except (IOError, struct.error) as err:
                     # Occasionally an error happens, try reconnect.
                     logger.warn(f"Reconnect after error: {err!r}")
-                    self.vpp_instance.disconnect()
+                    vpp_instance.disconnect()
                     # Testing shows immediate reconnect fails.
                     time.sleep(1)
-                    self.vpp_instance.connect_sync(u"csit_socket")
+                    vpp_instance.connect_sync(u"csit_socket")
                     logger.trace(u"Reconnected.")
                     reply = papi_fn(**command[u"api_args"])
             except (AttributeError, IOError, struct.error) as err:
@@ -558,6 +807,33 @@ class PapiSocketExecutor:
         return replies
 
 
+class Disconnector:
+    """Class for holding a single keyword."""
+
+    @staticmethod
+    def disconnect_all_papi_connections():
+        """Disconnect all connected client instances, tear down the SSH tunnels.
+
+        Also remove the local sockets by deleting the temporary directory.
+        Put disconnected client instances to the reuse list.
+        The added attributes are not cleaned up,
+        as their values will get overwritten on next connect.
+
+        Call this method just before killing/restarting all VPP instances.
+
+        This could be a class method of PapiSocketExecutor.
+        But Robot calls methods on instances, and it would be weird
+        to give node argument for constructor in import.
+        Also, as we have a class of the same name as the module,
+        the keywords defined on module level are not accessible.
+        """
+        cls = PapiSocketExecutor
+        # Iterate over copy of entries so deletions do not mess with iterator.
+        keys_copy = list(cls.conn_cache.keys())
+        for key in keys_copy:
+            cls.disconnect_by_key(key)
+
+
 class PapiExecutor:
     """Contains methods for executing VPP Python API commands on DUTs.
 
diff --git a/resources/libraries/python/VPPUtil.py b/resources/libraries/python/VPPUtil.py
index a7ec44c974..17043aa599 100644
--- a/resources/libraries/python/VPPUtil.py
+++ b/resources/libraries/python/VPPUtil.py
@@ -58,11 +58,15 @@ class VPPUtil:
     def restart_vpp_service(node, node_key=None):
         """Restart VPP service on the specified topology node.
 
+        Disconnect possibly connected PAPI executor.
+
         :param node: Topology node.
         :param node_key: Topology node key.
         :type node: dict
         :type node_key: str
         """
+        # Containers have a separate lifecycle, but better be safe.
+        PapiSocketExecutor.disconnect_all_sockets_by_node(node)
         DUTSetup.restart_service(node, Constants.VPP_UNIT)
         if node_key:
             Topology.add_new_socket(
@@ -85,11 +89,15 @@ class VPPUtil:
     def stop_vpp_service(node, node_key=None):
         """Stop VPP service on the specified topology node.
 
+        Disconnect possibly connected PAPI executor.
+
         :param node: Topology node.
         :param node_key: Topology node key.
         :type node: dict
         :type node_key: str
         """
+        # Containers have a separate lifecycle, but better be safe.
+        PapiSocketExecutor.disconnect_all_sockets_by_node(node)
         DUTSetup.stop_service(node, Constants.VPP_UNIT)
         if node_key:
             Topology.del_node_socket_id(node, SocketType.PAPI, node_key)
@@ -184,18 +192,28 @@ class VPPUtil:
                 VPPUtil.verify_vpp(node)
 
     @staticmethod
-    def vpp_show_version(node):
+    def vpp_show_version(
+            node, remote_vpp_socket=Constants.SOCKSVR_PATH, log=True):
         """Run "show_version" PAPI command.
 
+        Socket is configurable, so VPP inside container can be accessed.
+
         :param node: Node to run command on.
+        :param remote_vpp_socket: Path to remote socket to target VPP.
+        :param log: If true, show the result in Robot log.
         :type node: dict
+        :type remote_vpp_socket: str
+        :type log: bool
         :returns: VPP version.
         :rtype: str
+        :raises RuntimeError: If PAPI connection fails.
+        :raises AssertionError: If PAPI retcode is nonzero.
         """
         cmd = u"show_version"
-        with PapiSocketExecutor(node) as papi_exec:
+        with PapiSocketExecutor(node, remote_vpp_socket) as papi_exec:
             reply = papi_exec.add(cmd).get_reply()
-        logger.info(f"VPP version: {reply[u'version']}\n")
+        if log:
+            logger.info(f"VPP version: {reply[u'version']}\n")
         return f"{reply[u'version']}"
 
     @staticmethod
diff --git a/resources/libraries/python/topology.py b/resources/libraries/python/topology.py
index 2b930c08dc..c39e5afabb 100644
--- a/resources/libraries/python/topology.py
+++ b/resources/libraries/python/topology.py
@@ -1139,4 +1139,5 @@ class Topology:
         """
         for node in nodes.values():
             if u"sockets" in list(node.keys()):
+                # Containers are disconnected and destroyed already.
                 node.pop(u"sockets")