Register AWS EC2 instance in HAProxy.

haproxy-ec2-register.sh

#!/bin/bash

set -e

region=eu-central-1
haproxy_url=http://haproxy.internal:5555
haproxy_username=admin
haproxy_password=password
cluster_size=3

ACTION="$1"
BACKEND_NAME="$2"
BACKEND_PORT="$3"
VER_RETRIES=${cluster_size}
RETRIES=${cluster_size}
RANDOM=$$
SLEEP_MIN=1
SLEEP_MAX=${cluster_size}

PRIVATE_IP=$(curl -s http://169.254.169.254/latest/meta-data/local-ipv4)
INSTANCE_ID=$(curl -s http://169.254.169.254/latest/meta-data/instance-id)
REGION=$(curl -s http://169.254.169.254/latest/meta-data/placement/availability-zone | sed 's/[a-z]$//')
INSTANCE_NAME=$(aws ec2 describe-tags --region="$REGION" --filters "Name=resource-id,Values=$INSTANCE_ID" Name=key,Values=Name --query Tags[].Value --output text)

haproxyConfVersion() {
  VER_RES=$(curl -s -w '\n%{http_code}' -X GET --user "${haproxy_username}:${haproxy_password}" "${haproxy_url}/v1/services/haproxy/configuration/servers?backend=$BACKEND_NAME")
  VER_RES_CODE=$(echo "$VER_RES" | tail -1)
  if [ "$VER_RES_CODE" != "200" ]; then
    if [ $VER_RETRIES -gt 0 ]; then
      VER_RETRIES=$((VER_RETRIES - 1))
      echo >&2 'WARNING: Failed to fetch HAProxy configuration version. Retrying.'
      sleep $((RANDOM % SLEEP_MAX + SLEEP_MIN))
      haproxyConfVersion
      return $?
    fi
    echo >&2 'ERROR: Failed to fetch HAProxy configuration version.'
    return 2
  fi

  echo "$VER_RES" | head -1 | jq -r '._version'
  return 0
}

haproxyServerExists() {
  RESPONSE_CODE=$(
    curl -s -o /dev/null -w %{http_code} -X GET \
      --user "${haproxy_username}:${haproxy_password}" \
      "${haproxy_url}/v1/services/haproxy/configuration/servers/$INSTANCE_NAME?backend=$BACKEND_NAME"
  )
  if [ "$RESPONSE_CODE" = "200" ]; then
    echo 'true'
  else
    echo 'false'
  fi
}

haproxyRegister() {
  HAPROXY_BE_VERSION=$(haproxyConfVersion)
  if [ "$HAPROXY_BE_VERSION" = "null" ] || [ "$HAPROXY_BE_VERSION" = "" ]; then
    echo >&2 'ERROR: HAProxy configuration version is invalid.'
    exit 1
  fi
  RESPONSE_CODE=$(
    curl -s -o /dev/null -w %{http_code} -X POST \
      --user "${haproxy_username}:${haproxy_password}" \
      -H "Content-Type: application/json" \
      -d "{\"address\":\"$PRIVATE_IP\",\"check\":\"enabled\",\"cookie\":\"A\",\"name\":\"$INSTANCE_NAME\",\"port\":$BACKEND_PORT}" \
      "${haproxy_url}/v1/services/haproxy/configuration/servers?force_reload=true&version=$HAPROXY_BE_VERSION&backend=$BACKEND_NAME"
  )

  if [ "$RESPONSE_CODE" != "201" ] || [ "$(haproxyServerExists)" = "false" ]; then
    if [ $RETRIES -gt 0 ]; then
      RETRIES=$((RETRIES - 1))
      echo >&2 'WARNING: Failed to register the instance in HAProxy. Retrying.'
      sleep $((RANDOM % SLEEP_MAX + SLEEP_MIN))
      haproxyRegister
      return $?
    fi
    echo >&2 'ERROR: Failed to register the instance in HAProxy.'
    return 2
  fi

  return 0
}

haproxyUnregister() {
  HAPROXY_BE_VERSION=$(haproxyConfVersion)
  if [ "$HAPROXY_BE_VERSION" = "null" ] || [ "$HAPROXY_BE_VERSION" = "" ]; then
    echo >&2 'ERROR: HAProxy configuration version is invalid.'
    exit 1
  fi
  RESPONSE_CODE=$(
    curl -s -o /dev/null -w %{http_code} -X DELETE \
      --user "${haproxy_username}:${haproxy_password}" \
      "${haproxy_url}/v1/services/haproxy/configuration/servers/$INSTANCE_NAME?force_reload=true&version=$HAPROXY_BE_VERSION&backend=$BACKEND_NAME"
  )
  if [ "$RESPONSE_CODE" != "204" ] || [ "$(haproxyServerExists)" = "true" ]; then
    if [ $RETRIES -gt 0 ]; then
      RETRIES=$((RETRIES - 1))
      echo >&2 'WARNING: Failed to unregister the instance in HAProxy. Retrying.'
      sleep $((RANDOM % SLEEP_MAX + SLEEP_MIN))
      haproxyUnregister
      return $?
    fi
    echo >&2 'ERROR: Failed to unregister the instance in HAProxy.'
    return 2
  fi

  return 0
}

if [ "$ACTION" = "unregister" ]; then
  haproxyUnregister && echo "Instance $INSTANCE_NAME unregistered from $BACKEND_NAME." || (
    echo "ERROR: Failed to unregister instance $INSTANCE_NAME from $BACKEND_NAME."
    exit 1
  )
else
  haproxyRegister && echo "Instance $INSTANCE_NAME registered in $BACKEND_NAME." || (
    echo "ERROR: Failed to register instance $INSTANCE_NAME in $BACKEND_NAME."
    exit 1
  )
fi