Init container to wait for rabbit-mq readiness - docker

Question

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.

Answer 1

The following works without any extra images/scripts, but requires you to enable the Management Plugin, eg by using the rabbitmq:3.8-management image instead of eg rabbitmq:3.8.
initContainers:
- name: check-rabbitmq-ready
image: busybox
command: [ 'sh', '-c',
'until wget http://guest:guest#rabbitmq:15672/api/aliveness-test/%2F;
do echo waiting for rabbitmq; sleep 2; done;' ]
Specifically, this is waiting until the HTTP Management API is available, and then checking that the default vhost is running healthily. The %2F refers to the default / vhost, which has to be urlendoded. If using your own vhost, enter that instead.

Answer 2

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:
...