Use a static UID and GID

[stevehipwell]

The general consensus of Docker best practices include running as a non-root user and using a high static UID and GID (hexops/dockerfile for reference). It would be great if the Fluentd docker image is updated to provide a static UID and GID; this shouldn't have any impact on existing use but should make using the image in systems such as Kubernetes easier and more deterministic.

This is related to issue #48 but I think it deserves it's own issue to track the work.

[stevehipwell]

I think this is also related to #173, @repeatedly @edsiper would you be interested in a PR to set fixed UID and GID values?

[repeatedly]

We moved account setup to runtime by #78 before.
This trick is now not needed, right?

[stevehipwell]

@repeatedly the changes in that PR around UID and GID (actually GID wasn't set) appear to have been undone. I assume because the change of UID in entrypoint would need root access.

My preference would be to set an absolute UID and GID in the dockerfile. This would work well with K8s and doesn't need any extra permissions at runtime.

[stevehipwell]

@repeatedly @edsiper the current behaviour on Alpine doesn't look correct, as the user's group doesn't seem to be set to fluent. I suspect that -g might have been used where -G should have been used?

fluentd-docker-image/Dockerfile.template.erb

Line 167 in 06b0360

RUN addgroup -S fluent && adduser -S -g fluent fluent \

This results in the following output.

PS ~> docker run --rm -it --entrypoint /bin/sh fluent/fluentd:v1.14
$ id
uid=100(fluent) gid=65533(nogroup) groups=65533(nogroup)

If changes are needed here it'd be great if at same time the user uid (e.g. adduser -S -G fluent -u 1000 fluent) and group gid (e.g. addgroup -S -g 1000 fluent) could be set to absolute values?

[stevehipwell]

@kenhys are you in a position to comment on #245 (comment)?

[kenhys]

the current behaviour on Alpine doesn't look correct, as the user's group doesn't seem to be set to fluent. I suspect that -g might have been used where -G should have been used?

% docker run -u root --rm -it fluent/fluentd:v1.14-1  /bin/sh
/ # id fluent
uid=100(fluent) gid=65533(nogroup) groups=65533(nogroup),65533(nogroup)
/ # adduser -S -g fluent foo
/ # id foo
uid=101(foo) gid=65533(nogroup) groups=65533(nogroup),65533(nogroup)
/ # adduser -S -G fluent bar
/ # id bar
uid=102(bar) gid=101(fluent) groups=101(fluent),101(fluent)

Surely, -G should be used in this case.

[stevehipwell]

Thanks @kenhys.

[stevehipwell]

@kenhys now that the GID is being set how about making the UID & GID values absolute even if they're set to the current implicit values?