[conmon] pass custom --log-opt

[tobwen]

/kind feature

Description
It would be nice to pass custom --log-opt to conmon. That way, I could finish containers/conmon#273

Example

--log-opt="message-prefix={{.Name}}[{{.Tag}}]"
or
--log-opt="message-prefix=podman-nginx[test-build-20210706]"

to get

Jun 7 00:00:00 debian conmon[666]: podman-nginx[test-build-20210706] message

[haircommander]

would you be interested in submitting a patch :)

[tobwen]

would you be interested in submitting a patch :)

Trust me, you really don't want me to mess around in GO. But I can give it a try.

[tobwen]

Okay, here we go... WIP

https://github.com/containers/podman/blob/master/pkg/bindings/containers/types.go#L13

type LogOptions struct {
        Follow     *bool
        PrefixMsg  *string // new, to prefix a string (e.g. a name, an ID or anything else) to the message
        Since      *string
        Stderr     *bool
        Stdout     *bool
        Tail       *string
        Timestamps *bool
        Until      *string
}

https://github.com/containers/podman/blob/master/cmd/podman/common/specgen.go#L593

	logOpts := make(map[string]string)
	for _, o := range c.LogOptions {
		split := strings.SplitN(o, "=", 2)
		if len(split) < 2 {
			return errors.Errorf("invalid log option %q", o)
		}
		switch strings.ToLower(split[0]) {
		case "driver":
			s.LogConfiguration.Driver = split[1]
		case "path":
			s.LogConfiguration.Path = split[1]
		case "prefixmsg":
			s.LogConfiguration.PrefixMsg = split[1]
		case "max-size":
			logSize, err := units.FromHumanSize(split[1])
			if err != nil {
				return err
			}
			s.LogConfiguration.Size = logSize
		default:
			logOpts[split[0]] = split[1]
		}
	}

https://github.com/containers/podman/blob/master/pkg/specgen/specgen.go#L13

//  LogConfig describes the logging characteristics for a container
type LogConfig struct
	// LogDriver is the container's log driver.
	// Optional.
	Driver string `json:"driver,omitempty"`
	// LogPath is the path the container's logs will be stored at.
	// Only available if LogDriver is set to "json-file" or "k8s-file".
	// Optional.
	Path string `json:"path,omitempty"`
	// Prefix a string (e.g. a name, an ID or anything else) to the message
	// Optional.
	PrefixMsg string `json:"prefixmsg,omitempty"`
	// Size is the maximum size of the log file
	// Optional.
	Size int64 `json:"size,omitempty"`
	// A set of options to accompany the log driver.
	// Optional.
	Options map[string]string `json:"options,omitempty"`
}

@haircommander PTAL
Which name would be "nice" and "compatible"?

[tobwen]

Sorry, I'm stuck here. Maybe I'll make it an environment variable for conmon or just apply the changes to my own builds.

[rhatdan]

Isn't this what tag does?

man podman run
...
   --log-opt=name=value
       Logging driver specific options.

       Set custom logging configuration. The following *name*s are supported:

       path: specify a path to the log file
           (e.g. --log-opt path=/var/log/container/mycontainer.json);

       max-size: specify a max size of the log file
           (e.g. --log-opt max-size=10mb);

       tag: specify a custom log tag for the container
          (e.g. --log-opt tag="{{.ImageName}}".

[tobwen]

Isn't this what tag does?

No, see my report on conmon. The tag ends up in a journald variable, which is pretty costly to extract (see rsyslog docs on their journald module for example).

My approach just prefixes the important stuff to the syslog message, which is processed by default and at high performance.

But I am making use of the tag, of course. All that is missing is a switch to change the behavior to not break default logging (see the PR in conmon).

[mheon]

Passing new log options is pretty cheap on the Podman side, so long as Conmon is capable of interpreting them correctly (that would be a @haircommander question)

[tobwen]

Passing new log options is pretty cheap on the Podman side, so long as Conmon is capable of interpreting them correctly (that would be a @haircommander question)

Pretty cheap for someone who's into it :-) I'd extent Conmon of course. But I wanted to check if it's possible to get a podmon switch at all. Without it, I would only patch it for my own use (because nobody else would be able to access it).

[tobwen]

@mheon
Could you guide me, how to integrate new log options (as you can see, I already tried) Then I could finish it and present it to you.

[tobwen]

Implementation is too complicated and the audience is too little. Closing.