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43 lines
1.7 KiB
Markdown
43 lines
1.7 KiB
Markdown
---
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title: Following Log Files on Disk
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---
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# Following Log Files on Disk
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Some containers do not write logs to `sysout` or `syserr`. Many folks have asked if Dozzle can also show logs that are written to files. Unfortunately, files in containers are not accessible to other containers, so Dozzle wouldn't have a way to access these files. Dozzle can only access logs written to `sysout` or `syserr`, which is the same functionality as the `docker logs` command.
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If you are creating a service using Docker, then make sure to write logs to streams. An application should not attempt to write to logfiles. Instead, delegate the logging to Docker. The [twelve factor app](https://12factor.net/logs) has a great principle around logging that explains the importance of this principle.
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However, there are workarounds to be able to still access files using mounts.
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## Mounting Local Log Files with Alpine
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Dozzle reads any output stream. This can be used in combination with Alpine to `tail` a mounted file. An example of this is as follows:
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::: code-group
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```sh
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docker run -v /var/log/system.log:/var/log/test.log alpine tail -f /var/log/test.log
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```
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```yaml [docker-compose.yml]
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services:
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dozzle-from-file:
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container_name: dozzle-from-file
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image: alpine
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volumes:
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- /var/log/system.log:/var/log/stream.log
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command:
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- tail
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- -f
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- /var/log/stream.log
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network_mode: none
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restart: unless-stopped
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```
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:::
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In the above example, `/var/log/system.log` is mounted from the host and used with `tail -f` to follow the file. `tail` is smart to follow log rotations. During testing, using Alpine used about `~50KB` of memory.
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The second tab shows a `docker-compose` file which is useful if you want the log stream to survive server reboot.
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