generate tuned daemon.json

generate-dockerd-config.sh

#!/bin/sh
#
# This script generates a /etc/docker/daemon.json file tuned for the current environment.
# Currently, only the mtu option is suaported.
#
# Usefull for the developers who use Docker-in-Docker feature in their dev containers with VS Code and
# need to set the mtu option for the inner Docker daemon.
#
# This script is intended to be run using a DevContainer feature like script_runner.
# See https://github.com/wxw-matt/devcontainer-features for more details.


if ! command -v dockerd > /dev/null; then
  echo "dockerd command not found. Please install Docker first."
  exit 0
fi

if [ -f /etc/docker/daemon.json ]; then
  echo "File /etc/docker/daemon.json already exists. Exiting."
  exit 0
fi

generate_mtu_config() {
  # find default route interface
  default_route_interface="$(ip route show default | sed -e 's/^.*dev //' -e 's/ .*$//')"
  [ -z "$default_route_interface" ] && return

  eval "$(ip link show "$default_route_interface" | grep -o "mtu [0-9]\{1,\}" | tr ' ' '=')"
  if [ "$mtu" ] && [ "$mtu" -ne 1500 ]; then
    echo "    \"mtu\": $mtu,"
  fi
}

if [ "$(id -u)" -ne 0 ]; then
  sudo=sudo
 fi

mkdir -p /etc/docker
{
  echo '{'
  {
    generate_mtu_config
  } | sed '$ s/,$//'
  echo '}'
} | $sudo tee /etc/docker/daemon.json > /dev/null 2>&1