[memory_checker] Do not check memory usage of containers which are no…

…t created (sonic-net#11129)

Signed-off-by: Yong Zhao yozhao@microsoft.com

Why I did it
This PR aims to fix an issue (sonic-net#10088) by enhancing the script memory_checker.

Specifically, if container is not created successfully during device is booted/rebooted, then memory_checker do not need check its memory usage.

How I did it
In the script memory_checker, a function is added to get names of running containers. If the specified container name is not in current running container list, then this script will exit without checking its memory usage.

How to verify it
I tested on a lab device by following the steps:

Stops telemetry container with command sudo systemctl stop telemetry.service

Removes telemetry container with command docker rm telemetry

Checks whether the script memory_checker ran by Monit will generate the syslog message saying it will exit without checking memory usage of telemetry.

files/image_config/monit/memory_checker

@@ -25,6 +25,8 @@ import sys
 import syslog
 import re
 
+import docker
+
 
 def get_command_result(command):
     """Executes the command and return the resulting output.
@@ -86,14 +88,36 @@ def check_memory_usage(container_name, threshold_value):
             print("[{}]: Memory usage ({} Bytes) is larger than the threshold ({} Bytes)!"
                   .format(container_name, mem_usage_bytes, threshold_value))
             syslog.syslog(syslog.LOG_INFO, "[{}]: Memory usage ({} Bytes) is larger than the threshold ({} Bytes)!"
-                  .format(container_name, mem_usage_bytes, threshold_value))
+                          .format(container_name, mem_usage_bytes, threshold_value))
             sys.exit(3)
     else:
         syslog.syslog(syslog.LOG_ERR, "[memory_checker] Failed to retrieve memory value from '{}'"
                       .format(mem_usage))
         sys.exit(4)
 
 
+def get_running_container_names():
+    """Retrieves names of running containers by talking to the docker daemon.
+
+    Args:
+        None.
+
+    Returns:
+        running_container_names: A list indicates names of running containers.
+    """
+    try:
+        docker_client = docker.DockerClient(base_url='unix://var/run/docker.sock')
+        running_container_list = docker_client.containers.list(filters={"status": "running"})
+        running_container_names = [ container.name for container in running_container_list ]
+    except (docker.errors.APIError, docker.errors.DockerException) as err:
+        syslog.syslog(syslog.LOG_ERR,
+                      "Failed to retrieve the running container list from docker daemon! Error message is: '{}'"
+                      .format(err))
+        sys.exit(5)
+
+    return running_container_names
+
+
 def main():
     parser = argparse.ArgumentParser(description="Check memory usage of a container \
             and an alerting message will be written into syslog if memory usage \
@@ -104,7 +128,13 @@ def main():
     parser.add_argument("threshold_value", type=int, help="threshold value in bytes")
     args = parser.parse_args()
 
-    check_memory_usage(args.container_name, args.threshold_value)
+    running_container_names = get_running_container_names()
+    if args.container_name in running_container_names:
+        check_memory_usage(args.container_name, args.threshold_value)
+    else:
+        syslog.syslog(syslog.LOG_INFO,
+                      "[memory_checker] Exits without checking memory usage since container '{}' is not running!"
+                      .format(args.container_name))
 
 
 if __name__ == "__main__":