Working out why it is not behaving.
WHAT TO CHECK FIRST
Whether it is running, or restarting repeatedly.
HOW
List containers, including stopped ones, and read the status.
WHAT A RESTART LOOP INDICATES
The process is exiting immediately.
WHAT TO DO
Read the logs from the last attempt.
WHAT THE COMMON CAUSES ARE
A missing environment variable A file or permission problem A dependency not yet available The command being wrong
WHAT TO DO ABOUT THE LAST ONE
Run the image with a shell instead of its normal command.
WHY THAT HELPS
You can look around inside without the application starting.
WHAT TO DO IN A RUNNING CONTAINER
Execute a shell inside it.
WHAT TO CHECK THERE
Environment variables Files and their permissions Whether it can reach other services What is listening
WHAT TO DO WHEN THERE IS NO SHELL
Use a debug container sharing the same namespaces.
WHY MINIMAL IMAGES COMPLICATE THIS
They deliberately contain no tools.
WHAT TO INSPECT FROM OUTSIDE
The container's configuration, as the engine sees it.
WHAT THAT SHOWS
Mounts, networks, environment and the resolved command.
WHAT TO CHECK ABOUT EXITS
The exit code.
WHAT A HUNDRED AND THIRTY-SEVEN USUALLY MEANS
Terminated for exceeding memory.
