Init container to wait for rabbit-mq readiness

I saw the example for docker healthcheck of RabbitMQ at docker-library/healthcheck.

I would like to apply a similar mechanism to my Kubernetes deployment to await on Rabbit deployment readiness. I'm doing a similar thing with MongoDB, using a container that busy-waits mongo with some ping command.

apiVersion: apps/v1
kind: Deployment
metadata:
  name: app-1
spec:
  replicas: 1
  selector:
    matchLabels:
      app: app-1
  template:
    metadata:
      labels:
        app: app-1
    spec:
      initContainers:
        - name: wait-for-mongo
          image: gcr.io/app-1/tools/mongo-ping
      containers:
        - name: app-1-service
          image: gcr.io/app-1/service
          ...

However when I tried to construct such an init container I couldn't find any solution on how to query the health of rabbit from outside its cluster.

Solution

Adapted from this example, as suggested by @Hanx:

Dockerfile

FROM python:3-alpine

ENV RABBIT_HOST="my-rabbit"
ENV RABBIT_VHOST="vhost"
ENV RABBIT_USERNAME="root"

RUN pip install pika

COPY check_rabbitmq_connection.py /check_rabbitmq_connection.py
RUN chmod +x /check_rabbitmq_connection.py

CMD ["sh", "-c", "python /check_rabbitmq_connection.py --host $RABBIT_HOST --username $RABBIT_USERNAME --password $RABBIT_PASSWORD --virtual_host $RABBIT_VHOST"]

check_rabbitmq_connection.py

#!/usr/bin/env python3
# Check connection to the RabbitMQ server
# Source: https://blog.sleeplessbeastie.eu/2017/07/10/how-to-check-connection-to-the-rabbitmq-message-broker/

import argparse
import time
import pika

# define and parse command-line options
parser = argparse.ArgumentParser(description='Check connection to RabbitMQ server')
parser.add_argument('--host', required=True, help='Define RabbitMQ server hostname')
parser.add_argument('--virtual_host', default='/', help='Define virtual host')
parser.add_argument('--port', type=int, default=5672, help='Define port (default: %(default)s)')
parser.add_argument('--username', default='guest', help='Define username (default: %(default)s)')
parser.add_argument('--password', default='guest', help='Define password (default: %(default)s)')
args = vars(parser.parse_args())

print(args)

# set amqp credentials
credentials = pika.PlainCredentials(args['username'], args['password'])
# set amqp connection parameters
parameters = pika.ConnectionParameters(host=args['host'], port=args['port'], virtual_host=args['virtual_host'], credentials=credentials)

# try to establish connection and check its status
while True:
    try:
        connection = pika.BlockingConnection(parameters)
        if connection.is_open:
            print('OK')
            connection.close()
            exit(0)
    except Exception as error:
        raise
        print('No connection yet:', error.__class__.__name__)
        time.sleep(5)

Build and run:

docker build -t rabbit-ping .

docker run --rm -it \
    --name rabbit-ping \
    --net=my-net \
    -e RABBIT_PASSWORD="<rabbit password>" \
    rabbit-ping

and in deployment.yaml:

apiVersion: apps/v1
kind: Deployment
...
spec:
  ...
  template:
    ...
    spec:
      initContainers:
        - name: wait-for-rabbit
          image: gcr.io/my-org/rabbit-ping
          env:
            - name: RABBIT_PASSWORD
              valueFrom:
                secretKeyRef:
                  name: rabbit
                  key: rabbit-password
      containers:
        ...