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MONITOR.md

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Container Monitor

Container monitoring script is present as a service to update Consul metadata with current state of a service.

It is triggered via OnFailure and OnSuccess in service Unit definition and updates the JSON service definition in /etc/consul based on currently used binary.

 > sudo systemctl -ocat status monitor-beacon-node-sepolia-stable.service
○ monitor-beacon-node-sepolia-stable.service - Monitor for beacon-node-sepolia-stable that updates Consul
     Loaded: loaded (/etc/systemd/system/monitor-beacon-node-sepolia-stable.service; enabled; vendor preset: enabled)
     Active: inactive (dead) since Mon 2024-03-11 13:41:54 UTC; 2s ago
       Docs: https://github.com/status-im/infra-role-beacon-node-linux
    Process: 2010090 ExecStart=/data/beacon-node-sepolia-stable/monitor.sh (code=exited, status=0/SUCCESS)
   Main PID: 2010090 (code=exited, status=0/SUCCESS)
        CPU: 42ms

Started Monitor for beacon-node-sepolia-stable that updates Consul.
Changes detected, reloading Consul.
monitor-beacon-node-sepolia-stable.service: Deactivated successfully.

Known Issues

The method of modifying JSON files in /etc/consul using sed is crude but simple. It avoids the need to have to call Consul Catalog API with the whole set of service metadata only to update a single ServiceMeta key.

But there are a few problems with this approach:

  • It only works for metadata fields that are already present in the JSON file.
  • It causes Ansible to overwrite the fields, setting them to unknown.
  • It can fail due to JSON file format changes.