Fluentd not capturing docker logs

[de...@sofdesk.com]

Hi all,

I'm stuck at step 3 of the docker logging guide https://www.fluentd.org/guides/recipes/docker-logging .

My setup:

I'm running the `td-agent` with systemd (as documented in the quick start guide).

- My service file configuration: https://gist.github.com/devon-sofdesk/4670e5cae3baee580fbfab79e6915fc7

- My fluentd conf (taken from the docker guide)

```

[root@ip-172-31-39-98 td-agent]# cat td_input_docker.conf 

<source>

  @type forward

  port 24224

  bind 0.0.0.0

</source>

<match *.*>

  @type stdout

</match>

```

The Problem:

The docker run command isn't being logged in the td-agent log file `docker run --log-driver=fluentd ubuntu echo 'Hello Fluentd!'`

The log file only contains error messages saying that it can't match any patterns:
```

[root@ip-172-31-39-98 td-agent]# tail -n 6 -f /var/log/td-agent/td-agent.log 

2019-04-08 20:36:51 +0000 [warn]: #0 no patterns matched tag="1f165a460ccd"

2019-04-08 20:36:51.964595043 +0000 fluent.warn: {"tag":"1f165a460ccd","message":"no patterns matched tag=\"1f165a460ccd\""}

2019-04-08 21:36:54 +0000 [warn]: #0 no patterns matched tag="5bfb2b2fd881"

2019-04-08 21:36:54.185478907 +0000 fluent.warn: {"tag":"5bfb2b2fd881","message":"no patterns matched tag=\"5bfb2b2fd881\""}

2019-04-08 21:37:26 +0000 [warn]: #0 no patterns matched tag="3f641ef36f12"

2019-04-08 21:37:26.698440917 +0000 fluent.warn: {"tag":"3f641ef36f12","message":"no patterns matched tag=\"3f641ef36f12\""}

```

Attempted solutions:

- Specifying the fluentd server `ip:port` made no difference:

```docker run --log-driver=fluentd --log-opt fluentd-address=127.0.0.1:24224 ubuntu echo "TESTLOG"```

- I tried a `tailf -f /proc/<fluentd-PID>/fd/1` then I ran

```docker run --log-driver=fluentd --log-opt fluentd-address=0.0.0.0:24224 ubuntu echo "TESTEST"```

But nothing showed up in the stdout of the process...

I pretty much followed the same steps in the tutorial, but tweaked them to use systemd instead of running the td-agent in the foreground. Any one have an idea why the `td-agent` isn't logging the docker container stdout?

[Mr. Fiber]

Ah, recent docker logging driver removes "docker" prefix from tag.

You need to add tag with --log-opt like below:

docker run --log-driver=fluentd --log-opt tag="docker.{{.ID}}"

https://docs.docker.com/v17.09/engine/admin/logging/log_tags/

We will update the article.

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[de...@sofdesk.com]

Thanks @repeatedly, that solved the issue. 

Now to test with AWS ECS to see if it still works...

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