Build on EC2 agent is canceled: Agent <agent_name> unregistered: Agent has unregistered

Symptoms

Affected versions: 2024.07, 2024.12

The build is cancelled for the following reason:

Canceled: 
Agent <agent_name> unregistered: Agent has unregistered

teamcity-clouds.log indicates that the agent instance was terminated due to the Additional terminate conditions: After the first build condition set in the cloud profile settings, even though the first build hasn't finished:

[2025-02-02 08:28:31,932]   INFO [uled executor 3] - l.instances.StopInstanceAction - Terminating instance '<...', profile '...'{id=..., projectId=...}, reason: "After the first build"

Cause

The build agent process crashes inside the EC2 VM.

Resolution

1. Disable the Additional terminate conditions: After the first build condition in the cloud profile settings.
2. Set the Terminate instance idle time option to allow enough time to grab agent logs.
3. Download the logs from the agent from <Agent home directory>/logs.
4. Investigate the reason for the crash in the agent logs.
5. Submit a support request if you're unable to identify the cause of the crash and attach the collected build agent logs.