enable docker support in docker image

[helmut72]

When starting with this compose:

    image: ghcr.io/hsn723/postfix_exporter
    command: --docker.enable

log output is:

postfix_exporter: error: unknown long flag '--docker.enable', try --help

Only kubernetes is there. Would be cool to have docker support in a docker image too ;) Make really sense. Thanks.

[dosubot]

Hi @helmut72! I'm Dosu and I’m helping the postfix_exporter team.

Docker support (the --docker.enable flag) is implemented in the postfix_exporter codebase, but the official Docker image is built without Docker support due to the nodocker build tag. That's why you see "unknown long flag '--docker.enable'"—the flag isn't available in the published image. To use Docker log ingestion, you need to build postfix_exporter yourself without the nodocker tag, or use a binary variant like postfix_exporter_docker or postfix_exporter_aio that includes Docker support. The default image only supports reading logs from a file, so the recommended approach is to have Postfix write logs to a shared volume that postfix_exporter can access and tail inside the container. More details are in the README and issue #109.

To reply, just mention @dosu.

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