Docker container filesystem running out of space - how to find out which container to blame and handle large container json logs

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Published on August 15th 2019 - Listed in Linux Rancher Containers Docker


Docker application container eating up disk space

Docker/application containers are not supposed to write on the local disk, at least in a perfect stateless container world. However it can still happen that the filesystem runs out of space (temporary files, application logs, etc). With a proper monitoring in place the warning is out in advance, so there's time to react.

root@dockerhost:~# df -h /var/lib/docker
Filesystem                    Type  Size  Used Avail Use% Mounted on
/dev/mapper/vgdocker-lvdocker ext4   50G   46G  1.6G  97% /var/lib/docker

Find the container(s) to blame

The docker command offers a sub-command "system" which can help identify how much disk space is used by the container eco-system. However this command is only partly helpful, as long as the data resides within the container's file system:

root@dockerhost:~# docker system df
TYPE                TOTAL               ACTIVE              SIZE                RECLAIMABLE
Images              43                  43                  15.55GB             5.102GB (32%)
Containers          57                  56                  346.2MB             0B (0%)
Local Volumes       5                   4                   56.68MB             36B (0%)
Build Cache         0                   0                   0B                  0B

The total collected size of roughly 16GB is nowhere near the used 46GB seen on the filesystem usage.

If the used disk space is not caused from within a container, the container files (outside of the container) should be checked, too:

root@dockerhost:~# du -ks /var/lib/docker/containers/* | sort -n  | tail
31096    /var/lib/docker/containers/51cdfabd2c18e509644454bd479c062582b55e6a5ee679256f2e4a6b3f523126
32180    /var/lib/docker/containers/723132a88b9a8a50f8a747875f01da1fe25497b8a9a47372c3eb96435bda777b
45180    /var/lib/docker/containers/3d739834517dbd76f8756e4280d42d1f7a6a369ef432afc228455001e903778d
51308    /var/lib/docker/containers/76d2ef75ae03b3bec362bdc135ec3add95c3bd8550b817a6a3373d493101fe0a
66768    /var/lib/docker/containers/0e0cfa9079f910438260cf76ac051e959f0d0f572893c130e790a912590d04db
433220    /var/lib/docker/containers/3422c8225917a8997444e20fbcbd93b2bc966775e63da1937b111675abf84273
436536    /var/lib/docker/containers/9ac37529eb51d5af264ebfd7b9288b9ba152d50739b8553e241cff3276cecb4c
567556    /var/lib/docker/containers/b444b0ce5972cb6639c12b610ee008845aded2baf991b64278443281460ea629
1103040    /var/lib/docker/containers/fabe6a6060e123733eb42560a9fbd178dd20a7955e4c8f45a7e38632ac4e498b
23962464    /var/lib/docker/containers/a17749f9a33b6501d8b48ee31591a0f27c9e472189b8f32a5e849fe6db419328

Indeed. Container a17749f9... uses a large part of the whole file system:

root@dockerhost:~# du -ksh /var/lib/docker/containers/a17749f9a33b6501d8b48ee31591a0f27c9e472189b8f32a5e849fe6db419328
23G    /var/lib/docker/containers/a17749f9a33b6501d8b48ee31591a0f27c9e472189b8f32a5e849fe6db419328

Looking inside this directory, it's easy to see that the container's "console" log file (stdout/stderr) is responsible for eating all this disk space:

root@dockerhost:~# ll /var/lib/docker/containers/a17749f9a33b6501d8b48ee31591a0f27c9e472189b8f32a5e849fe6db419328
total 23963048
-rw-r----- 1 root root 24538098764 Aug 15 07:46 a17749f9a33b6501d8b48ee31591a0f27c9e472189b8f32a5e849fe6db419328-json.log
drwx------ 2 root root        4096 Jul 19 14:50 checkpoints
-rw------- 1 root root        6579 Jul 19 14:50 config.v2.json
-rw-r--r-- 1 root root        1547 Jul 19 14:50 hostconfig.json
-rw-r--r-- 1 root root          13 Jul 19 14:50 hostname
-rw-r--r-- 1 root root         177 Jul 19 14:50 hosts
drwx------ 3 root root        4096 Jul 19 14:50 mounts
-rw-r--r-- 1 root root         111 Jul 19 14:50 resolv.conf
-rw-r--r-- 1 root root          71 Jul 19 14:50 resolv.conf.hash

If the json-file log is suspected from the beginning, the docker inspect command can be used to quickly check the log sizes across all containers:

root@dockerhost:~# docker inspect --format '{{.LogPath}}' $(docker ps --format '{{.ID}}') | xargs du -ks | sort -n  | tail
18760    /var/lib/docker/containers/b11aa795ce5bef78bf90c355cbcf7b47a565774654cb8443bc4c82d54c9e8569/b11aa795ce5bef78bf90c355cbcf7b47a565774654cb8443bc4c82d54c9e8569-json.log
24520    /var/lib/docker/containers/75bcb03368cab475b00e736e13c09a552c66db516ea7f217c313e9770cf314dd/75bcb03368cab475b00e736e13c09a552c66db516ea7f217c313e9770cf314dd-json.log
45140    /var/lib/docker/containers/3d739834517dbd76f8756e4280d42d1f7a6a369ef432afc228455001e903778d/3d739834517dbd76f8756e4280d42d1f7a6a369ef432afc228455001e903778d-json.log
51268    /var/lib/docker/containers/76d2ef75ae03b3bec362bdc135ec3add95c3bd8550b817a6a3373d493101fe0a/76d2ef75ae03b3bec362bdc135ec3add95c3bd8550b817a6a3373d493101fe0a-json.log
66760    /var/lib/docker/containers/0e0cfa9079f910438260cf76ac051e959f0d0f572893c130e790a912590d04db/0e0cfa9079f910438260cf76ac051e959f0d0f572893c130e790a912590d04db-json.log
433200    /var/lib/docker/containers/3422c8225917a8997444e20fbcbd93b2bc966775e63da1937b111675abf84273/3422c8225917a8997444e20fbcbd93b2bc966775e63da1937b111675abf84273-json.log
436524    /var/lib/docker/containers/9ac37529eb51d5af264ebfd7b9288b9ba152d50739b8553e241cff3276cecb4c/9ac37529eb51d5af264ebfd7b9288b9ba152d50739b8553e241cff3276cecb4c-json.log
567528    /var/lib/docker/containers/b444b0ce5972cb6639c12b610ee008845aded2baf991b64278443281460ea629/b444b0ce5972cb6639c12b610ee008845aded2baf991b64278443281460ea629-json.log
1103392    /var/lib/docker/containers/fabe6a6060e123733eb42560a9fbd178dd20a7955e4c8f45a7e38632ac4e498b/fabe6a6060e123733eb42560a9fbd178dd20a7955e4c8f45a7e38632ac4e498b-json.log
23968192    /var/lib/docker/containers/a17749f9a33b6501d8b48ee31591a0f27c9e472189b8f32a5e849fe6db419328/a17749f9a33b6501d8b48ee31591a0f27c9e472189b8f32a5e849fe6db419328-json.log

To immediately reduce the used disk space, the log can be cleared:

root@dockerhost:~# echo "" > /var/lib/docker/containers/a17749f9a33b6501d8b48ee31591a0f27c9e472189b8f32a5e849fe6db419328/a17749f9a33b6501d8b48ee31591a0f27c9e472189b8f32a5e849fe6db419328-json.log

And a lot of disk space is available again:

root@dockerhost:~# df -h /var/lib/docker
Filesystem                    Type  Size  Used Avail Use% Mounted on
/dev/mapper/vgdocker-lvdocker ext4   50G   22G   26G  47% /var/lib/docker

But this will happen again!

Yes, it probably will. Especially if the log file was full of stdout messages and the containers are in heavy use. So how can this be prevented from happening in the future?

The json-file logging method is the default setting for Docker container logging. And by default log entries are just appended into the containerid-json.log file. But json-file does support configuration parameters for log rotation and limits. From the documentation:

{
  "log-driver": "json-file",
  "log-opts": {
    "max-size": "10m",
    "max-file": "3"
  }
}

Setting log rotation and limits on container logging

Because this Docker environment is managed by Rancher 1.x, the log settings need to be adjusted in the service which starts these containers. In Rancher the container names contain the service name:

root@dockerhost:~# docker inspect --format '{{.Name}}' a17749f
/r-Q-Q-Server-8-1821ddd8

According to the nomenclature, the "Q-Server" service needs to be adjusted.

Rancher 1.x json-file log settings

In a standalone container environment managed by command line, you'd simply append the docker run command with the json-file settings:

root@dockerhost:~# docker run --log-opt max-size=500m --log-opt max-file=3 [...] imagename

After the service is upgraded, verify with docker inspect that the log options are active. Here the new container ID is checked, because (obviously) the containers of that service are newly deployed containers:

root@dockerhost:~# docker ps --filter 'name=r-Q-Q-Server-*' --format '{{.ID}}'
c2693d891c0f

root@dockerhost:~# docker inspect --format '{{.HostConfig.LogConfig}}' c2693d891c0f
{json-file map[max-file:3 max-size:500m]}

Great, the log options are active! From now on the container's json-file "console" log will be rotated when it reaches a size of 500MB and there will be a maximum of 3 log files (summa summarum: This should use maximum 1.5GB of disk space).


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