docker compose 3 sysctls directive unsupported

Question

I have a sysctls setting in docker-compose file, but as I understood, this directive is ignored in version 3:

sysctls:
        - net.core.somaxconn = 65536
        - net.ipv4.tcp_max_tw_buckets = 1440000
        - net.ipv4.ip_local_port_range = 1024 65000
        - net.ipv4.tcp_fin_timeout = 15
        - net.ipv4.tcp_window_scaling = 1
        - net.ipv4.tcp_max_syn_backlog = 3240000
        - fs.file-max = 20480

I need to find another way to set these parameters, but I can't exactly figure out how from the docs (tried RUN and CMD), and I need a clear example showing how to do this. I understand that normally from the command line it goes like this:

sudo sysctl -w net.core.somaxconn=65536

Thanks.

Answer 1

With version 3 docker-compose file, the option still works with docker-compose, but it does not work in docker swarm.

This option is ignored when deploying a stack in swarm mode with a (version 3) Compose file.

This is because sysctl reads and modifies the attributes of the system kernel, so running it in a container does not make sense. It's logical that docker swarm does not support it anymore because if you have 2 stacks / docker-compose.yml all using this instruction, there would be conflict.

So the only way to do it is to run the command on the host machine.