Networking & Remote Access on Flatcar Container Linux

DNS Configuration

Mon, 01 Jan 0001 00:00:00 +0000

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.

OverlayBD Artifact Streaming

Mon, 01 Jan 0001 00:00:00 +0000

Installation

Flatcar Container Linux offers support for the installation and customization of containerd’s accelerated container image artifact streaming. Both accelerated-container-image and the overlaybd back-end are combined in an optional, system dependent sysext .

The sysext can be provisioned simply by adding the line overlaybd to /etc/flatcar/enabled-sysext.conf. Since these sysexts are system dependent (compiled against the system’s C library), they will be updated automatically in lockstep with the operating system.

Example Butane configuration:

---
# config.yaml
# butane < config.yaml > config.json
variant: flatcar
version: 1.0.0

storage:
  files:
  - path: /etc/flatcar/enabled-sysext.conf
    contents:
      inline: |
        overlaybd

Usage

The below usage largely follows upstream’s Getting started guide .

Network configuration with networkd

Mon, 01 Jan 0001 00:00:00 +0000

Flatcar Container Linux machines are preconfigured with networking customized for each platform. You can write your own networkd units to replace or override the units created for each platform. This article covers a subset of networkd functionality. You can view the full docs here .

Drop a networkd unit in /etc/systemd/network/ or inject a unit on boot via a Butane Config. Files placed manually on the filesystem will need to reload networkd afterwards with sudo systemctl restart systemd-networkd. Network units injected via a Butane Config will be written to the system before networkd is started, so there are no work-arounds needed.

Handle ACPI events

Mon, 01 Jan 0001 00:00:00 +0000

acpid

Beginning with Flatcar major release 3255 acpid can be enabled at boot with Ignition.

This can be configured with a butane definition:

---
variant: flatcar
version: 1.0.0
systemd:
  units:
    - name: acpid.service
      enabled: true
storage:
  files:
    - path: /etc/acpi/events/default
      contents:
        inline: |
          event=.*
          action=/etc/acpi/default.sh %e

    - path: /etc/acpi/default.sh
      contents:
        inline: |
          set $*
          logger "ACPI event handled: $*"
      mode: 0744

This simple configuration will only log the handled ACPI events, example with QEMU: