DNS Configuration

    By default, DNS resolution on Flatcar Container Linux is handled through /etc/resolv.conf, which is a symlink to /run/systemd/resolve/resolv.conf. This file is managed by systemd-resolved . Normally, systemd-resolved gets DNS IP addresses from systemd-networkd , either via DHCP or static configuration. DNS IP addresses can also be set via systemd-resolved's resolved.conf . See Network configuration with networkd for more information on systemd-networkd.

    Using a local DNS cache

    systemd-resolved includes a caching DNS resolver. To use it for DNS resolution and caching, you must enable it via nsswitch.conf by adding resolve to the hosts section.

    Here is an example Container Linux Config snippet to do that:

    storage:
      files:
        - path: /etc/nsswitch.conf
          filesystem: root
          mode: 0644
          contents:
            inline: |
              # /etc/nsswitch.conf:
    
              passwd:      files usrfiles
              shadow:      files usrfiles
              group:       files usrfiles
    
              hosts:       files usrfiles resolve dns
              networks:    files usrfiles dns
    
              services:    files usrfiles
              protocols:   files usrfiles
              rpc:         files usrfiles
    
              ethers:      files
              netmasks:    files
              netgroup:    files
              bootparams:  files
              automount:   files
              aliases:     files
    

    Only nss-aware applications can take advantage of the systemd-resolved cache. Notably, this means that statically linked Go programs and programs running within Docker/rkt will use /etc/resolv.conf only, and will not use the systemd-resolve cache.