enable syslog logger to have access to env and labels

[flyinprogrammer]

- What I did
I added env and labels as valid log options for the syslog logger.

- How I did it
Well... there's only 1 commit, I reckon you can figure that out.

- How to verify it
You know I probably could write a test like this one: https://github.com/docker/docker/blob/master/daemon/logger/syslog/syslog_test.go#L40-L45

Or...

I could show you this:

Shell:

$ docker run -it --rm --log-driver syslog --log-opt tag="{{ (.ExtraAttributes nil).MESOS_TASK_ID }}" --log-opt env=MESOS_TASK_ID -e MESOS_TASK_ID=logtester.1234 flyinprogrammer/logtester
+ exec app
2016-04-01 15:22:17.075416751 +0000 UTC stderr msg: 1
2016-04-01 15:22:17.075416751 +0000 UTC stdout msg: 1
2016-04-01 15:22:22.075767762 +0000 UTC stderr msg: 2
2016-04-01 15:22:22.075767762 +0000 UTC stdout msg: 2

/var/log/syslog:

Apr  1 15:22:17 ip-10-27-39-73 docker/logtester.1234[45499]: + exec app
Apr  1 15:22:17 ip-10-27-39-73 docker/logtester.1234[45499]: 2016-04-01 15:22:17.075416751 +0000 UTC stderr msg: 1
Apr  1 15:22:17 ip-10-27-39-73 docker/logtester.1234[45499]: 2016-04-01 15:22:17.075416751 +0000 UTC stdout msg: 1
Apr  1 15:22:22 ip-10-27-39-73 docker/logtester.1234[45499]: 2016-04-01 15:22:22.075767762 +0000 UTC stderr msg: 2
Apr  1 15:22:22 ip-10-27-39-73 docker/logtester.1234[45499]: 2016-04-01 15:22:22.075767762 +0000 UTC stdout msg: 2

So this is pretty cool huh because it starts to address issues like this one:
mesosphere/marathon#717

So that's nifty huh 😸.

- A picture of a cute animal (not mandatory but encouraged)

Steve!

Signed-off-by: Alan Scherger flyinprogrammer@gmail.com

[LK4D4]

why not
LGTM

[thaJeztah]

@flyinprogrammer could you make sure to update the documentation as well to mention the new options? https://github.com/docker/docker/blob/master/docs/admin/logging/overview.md#syslog-options

[flyinprogrammer]

@thaJeztah is this good enough?

[calavera]

LGTM but it needs a rebase

[flyinprogrammer]

@calavera done 😄

[thaJeztah]

I built the docs for this, and I think we should wrap this, otherwise only a small part of the example is visible;

Also, I suggest to change the label name to something that more clearly stands out as being for "illustrational" purposes (e.g. SOME_ENV_VAR), so:

$ docker run -it --rm \
    --log-driver syslog \
    --log-opt tag="{{ (.ExtraAttributes nil).SOME_ENV_VAR }}" \
    --log-opt env=SOME_ENV_VAR \
    -e SOME_ENV_VAR=logtester.1234 \
    flyinprogrammer/logtester

(I like the idea of the log tester image BTW!)

[flyinprogrammer]

@thaJeztah thanks for the feedback! You should see your suggestions reflected in the latest push.

As for logtester, it's been pretty helpful for testing log flows, and I should have a post coming out soon where I use it to performance test rsyslog.

[thaJeztah]

@flyinprogrammer yes, it looks simple and useful, nice 👍

[thaJeztah]

LGTM

[vdemeester]

LGTM 🐮

[zquiring01]

@flyinprogrammer Is there any way to append the labels/environment variables outside of the --log-opt tag parameter? I noticed that the syslog logging driver supports the use of --log-opt label but in testing couldn't get the labels to output. Running the following test:

docker run
--label production_status="testing" -e os="windows"
--log-driver syslog --log-opt syslog-address=udp://0.0.0.0:514
--log-opt labels=production_status,os
--log-opt tag="foobar"
alpine echo hello world

returns:

<30>Aug 18 21:19:35 foobar[2542]: hello world

In this case I want the labels/environment variables to get included in the message section, as oppose to the header (the APP-NAME section).

[flyinprogrammer]

So this is still working as designed so far as I can tell:

docker run -it --rm \
--log-driver syslog \
--log-opt tag="{{ (.ExtraAttributes nil).production_status }}--{{ (.ExtraAttributes nil).os }}" \
--log-opt env=os \
--log-opt labels=production_status \
--label production_status="testing" \
--env os="windows" \
flyinprogrammer/logtester

generates:

Sep  2 14:16:42 <hostname> testing--windows[1717]: 2017-09-02 21:16:42.610942081 +0000 UTC stderr msg: 1
Sep  2 14:16:42 <hostname> testing--windows[1717]: 2017-09-02 21:16:42.610942081 +0000 UTC stdout msg: 1

You'll note that the magic of getting your variables into the APP-NAME section is done in --log-opt tag.
Which is documented here.

In this case I want the labels/environment variables to get included in the message section, as oppose to the header (the APP-NAME section).

In order to do this you would need to provide your own syslog format as we've done here to provide support for rfc3164, rfc5424, and rfc5424micro.