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content/blog/managing-mongodb-resource-usage-docker-compose.md

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+---
+title: "Limiting MongoDB Resource Usage within Docker Compose"
+date: 2023-09-19T16:08:41-04:00
+draft: false
+tags: []
+math: false
+medium_enabled: false
+---
+
+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.
+
+First, we can set some limits to container in general within docker-compose.
+
+Example:
+
+```yml
+mongo:
+  image: docker.io/mongo:5.0
+  mem_limit: 256m
+  cpus: 0.25
+```
+
+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. 
+
+To see a detailed list of possible options, check out the [docker documentation](https://docs.docker.com/config/containers/resource_constraints/).
+
+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.
+
+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.
+
+Luckily we can change this default, by adding a flag within the docker-compose file.
+
+```yml
+mongo:
+  image: docker.io/mongo:5.0
+  mem_limit: 256m
+  cpus: 0.25
+  command: --wiredTigerCacheSizeGB 0.25
+```
+
+The `wiredTigerCacheSizeGB` takes values between `0.25` GB and `10000` GB.
+