Debugging

deploy.update_config, credential_spec, ports[].mode: host: every one of these is valid against the compose-spec schema, and none of them has ever done anything to a plain docker compose up. They’re Swarm-only. Before Compose 5.6.0, a file carrying any of them loaded without complaint, and whatever behavior you expected from reading the spec just never showed up, with no hint why. What changed Load a file with one of these attributes now, and Compose says so: ...

depends_on reads fine when a Compose file has two or three services. Past that, tracing who starts after whom means scrolling between blocks and holding the chain in your head. docker compose alpha viz reads the same file and prints the graph instead. docker compose alpha viz What it prints Against a two-service file (web depending on db), the default output is a minimal Graphviz digraph: digraph "myapp" { layout=dot; "db" [style="filled" label=<<font point-size="15">db</font>>]; "web" [style="filled" label=<<font point-size="15">web</font>>]; "web" -> "db"; } Add --image, --ports, and --networks and each node’s label grows to match: ...

A failing lifecycle hook, post_start, pre_stop, or the new pre_start, used to report only its exit code: db hook exited with status 1 What the hook actually printed depended on how it ran. Under a plain docker compose up, the output streamed live to the terminal, mixed into the rest of up’s output, but was never carried into the error message itself. Under restart, run, or any tool driving Compose as a library, there was no listener attached at all, so Compose didn’t even request stdout or stderr from the daemon, and there was nothing to read afterward, live or otherwise. Since Compose 5.5.1, both cases keep a tail of the output and fold it straight into the error on failure. ...

docker compose down looks like a tidy shutdown command. It is, but the flags around it decide whether you walk away with your data intact, with a clean image store, or with a database wiped because you typed -v out of habit. The default behavior Without any flag, down stops and removes: Every container in the project The default network Compose created for the project Anonymous volumes that the stack was using It does not remove: ...

docker compose ps shows the services inside the current project. docker compose ls zooms out: every Compose stack running anywhere on the host, regardless of which directory you happen to be standing in. The basics Run it from any directory: docker compose ls Sample output: NAME STATUS CONFIG FILES api-platform running(4) /home/dev/api-platform/compose.yaml data-pipeline running(2) /home/dev/data-pipeline/compose.yaml old-prototype exited(3) /tmp/prototype/compose.yaml Three columns: the project name, how many services are up, and the path to the Compose file that started it. No need to cd into the project to see what’s running. ...