While configuring the (Docker) container Gateway, the docker service was restarted a few times and that created lots of container IDs in the cluster_info table of the SSG database. These invalid containers are also showing up in the policy manager dashboard.
All Supported Releases of API Gateway.
The Gateway has a process that cleans up this cluster_info table at regular intervals. This interval has a default value of 90 days and it can be configured by the "com.l7tech.server.clusterStaleNodeCleanupTimeoutSeconds" in the system.properties file. You can add this setting to the YAML file for docker containers.
The other option is to clear the entries manually from the cluster_info table in the Gateway MySQL database when needed.