Documented steps

Add a `sysctls:` block to the service using either array or map syntax.
Map form: `sysctls: { net.core.somaxconn: 1024, net.ipv4.tcp_syncookies: 0 }`.
Array form: `sysctls: - net.core.somaxconn=1024 - net.ipv4.tcp_syncookies=0`.
Run `docker compose up -d` and confirm with `docker compose exec <service> sysctl net.core.somaxconn`.
Official docs: https://docs.docker.com/reference/compose-file/services/#sysctls and https://docs.docker.com/engine/reference/commandline/run/ (namespaced-kernel-parameters)

Known gotchas

Only kernel parameters that are NAMESPACED in the kernel can be set inside a container; sysctls that would modify the host system are rejected.
Map and array forms are equivalent - pick one; do not mix both for the same key.
A sysctl that the host kernel or the container runtime does not permit produces a runtime error when the container starts.
sysctls is a mapping-type key for merge purposes (extends merges rather than replaces).

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Tune Linux capabilities in Docker Compose with cap_add and cap_drop (least-privilege hardening)

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Set kernel sysctls on a Docker Compose service

Documented steps

Known gotchas

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