Support `nerdctl logs` for the containers running without -d

[ningziwen]

What is the problem you're trying to solve

Support nerdctl logs for the containers running without -d

README.md already stated it is not supported yet. So opening a feature request instead of a bug report.

Reproducd by building source code from main branch.

$ sudo ./_output/nerdctl run -it ubuntu
# open a new terminal

$ sudo ./output/nerdctl ps # get the container id

$ sudo ./_output/nerdctl logs ccc97467def7
FATA[0000] failed to load logging config: failed to read log config file "/var/lib/nerdctl/1935db59/containers/default/ccc97467def7dd95330c6e872917e130180a1de2e4d6c34bdebeb16af434a5a6/log-config.json": open /var/lib/nerdctl/1935db59/containers/default/ccc97467def7dd95330c6e872917e130180a1de2e4d6c34bdebeb16af434a5a6/log-config.json: no such file or directory

Describe the solution you'd like

Add the feature to support logs command with the container running without -d.

Additional context

runfinch/finch#85

[ningziwen]

/assign

[ningziwen]

Trying error log tracing in nerdctl logs command.

nerdctl logs -> log_viewer.InitContainerLogViewer() -> logging.LoadLogConfig()

The error is failed in os.ReadFile(logConfigFilePath) without no such file or directory

The logConfigFilePath is the log-config.json in current container's dataStore dir.

log-config.json's directory of the container running by sudo ./_output/nerdctl run -it ubuntu

$ ls
hostname  oci-hook.createRuntime.log  resolv.conf

log-config.json's directory of the container running by sudo ./_output/nerdctl run -d ubuntu

$ ls
<id>-json.log  hostname  log-config.json  oci-hook.createRuntime.log  resolv.conf

Found the line to write log-config.json.

[ningziwen]

Just found this recent merged PR fixed the error. The log-config.json appears in the container ran by nerdctl run -it now.

However, there is no log in the container ran by nerdctl run -it.

Ran while true; do $(echo date); sleep 1; done in terminal of -it container. Then nerdctl logs returns empty.

Ran sudo ./_output/nerdctl -d ubuntu sh -c "while true; do $(echo date); sleep 1; done", then nerdctl logs returns printed date lines.

[yzxiu]

When the container is run with -it(or without -d)，log data is output to nerdctl process stdout.
If want to get logs through nerdctl logs, it may be necessary to copy the log to the log file(or other log drivers) in another goroutine.

[ningziwen]

Currently, -it uses the ioCreator to write stdOut to console.Current().

-d uses the ioCreator to write to uri.String().

[AkihiroSuda]

@ningziwen Do you still plan to work on this?

[ningziwen]

@ningziwen Do you still plan to work on this?

Yes but it will take some time. Feel free to take over if you have urgent need of this feature.

[danishprakash]

@ningziwen I can work on this if it's okay.

[ningziwen]

@danishprakash Sure go ahead.

[danishprakash]

I spent some time looking at this and based on what @ningziwen has already mentioned, I tried to create a multiwriter and create a ioCreator out of it but it's messy and didn't work primarily because uri.String() dir tree isn't setup yet or isn't the right path at the point of execution in NewTask.

@yzxiu when you say we need to copy the logs over explicitly, shouldn't that piece go into containerd? I'm new to this project so still trying to understand the demarcations. Sorry If I missed anything.

[fahedouch]

I tried to fix this here but stucked because of this <= containerd-dev slack thread

It looks like containerd io limitation