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45 lines
1.7 KiB
Markdown
45 lines
1.7 KiB
Markdown
---
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title: "Limiting MongoDB Resource Usage within Docker Compose"
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date: 2023-09-19T16:08:41-04:00
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draft: false
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tags:
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- Containers
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math: false
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medium_enabled: false
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---
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*Warning: This technique does not work for the older Docker Compose v3*
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One of my web services utilizes MongoDB as the database backend. It lives on one of the smaller sized virtual private servers with only 1GB of RAM and 1 CPU. Every so often I encounter a scenario where MongoDB is taking all of the sytem resources, so I started looking into how to limit it.
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First, we can set some limits to container in general within docker-compose.
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Example:
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```yml
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mongo:
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image: docker.io/mongo:5.0
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mem_limit: 256m
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cpus: 0.25
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```
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This says that the mongo container can only use a maximum of 256MB of memory and can only use up to 25% of one CPU.
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To see a detailed list of possible options, check out the [docker documentation](https://docs.docker.com/config/containers/resource_constraints/).
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Keep in mind that your memory and CPUs are not virtualized, therefore the container can see all the resources available, it just cannot request them.
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This may lead to some problems depending on the codebase. For example, in [MongoDB](https://www.mongodb.com/docs/manual/reference/configuration-options/#mongodb-setting-storage.wiredTiger.engineConfig.cacheSizeGB) the WiredTiger internal cache is by default set to 50% of the total amount of RAM minus 1GB.
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Luckily we can change this default, by adding a flag within the docker-compose file.
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```yml
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mongo:
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image: docker.io/mongo:5.0
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mem_limit: 256m
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cpus: 0.25
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command: --wiredTigerCacheSizeGB 0.25
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```
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The `wiredTigerCacheSizeGB` takes values between `0.25` GB and `10000` GB.
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