Docker-compose wait-to-start

ACCESS_ELASTIC.md

When unsing docker compose you can have a problem with the order of dependent linked containers

The solution is to start a script which tries to access a service and waits until it gets ready before loading your program

access_elastic_search.py

# This code needs to access elastic search!
from datetime import datetime
from elasticsearch import Elasticsearch
es = Elasticsearch('elastic')
es.index(index="my-index", doc_type="test-type", id=42, body={"any": "data", "timestamp": datetime.now()})
print es.get(index="my-index", doc_type="test-type", id=42)

docker-compose.yml

elastic:
    image: elasticsearch
    command: elasticsearch -Des.node.name="YourNodeName"
    ports:
       - "9200:9200"

app:
    image: ubuntu:14.04
    command: sh wait_to_start.sh
    working_dir: /src
    links:
        - elastic:elastic
    volumes:
        - .:/src
    environment:
        - WAIT_COMMAND=[ $(curl --write-out %{http_code} --silent --output /dev/null http://elastic:9200/_cat/health?h=st) = 200 ]
        - WAIT_START_CMD=python access_elastic_search.py
        - WAIT_SLEEP=2
        - WAIT_LOOPS=10

wait_to_start.sh

#!/bin/bash

echo $WAIT_COMMAND
echo $WAIT_START_CMD

is_ready() {
    eval "$WAIT_COMMAND"
}

# wait until is ready
i=0
while ! is_ready; do
    i=`expr $i + 1`
    if [ $i -ge $WAIT_LOOPS ]; then
        echo "$(date) - still not ready, giving up"
        exit 1
    fi
    echo "$(date) - waiting to be ready"
    sleep $WAIT_SLEEP
done

#start the script
exec $WAIT_START_CMD

Just thought I'd mention that you might be able to make this shorter by using timeout and until, something like:

timeout $WAIT_TIMEOUT bash -c "until $WAIT_COMMAND; do sleep $WAIT_SLEEP; done"

If you come across an error "Invalid interpolation format for "environment" option in service", you need to escape the $

environment:
  - WAIT_COMMAND=[ $$(curl --write-out %{http_code} --silent --output /dev/null http://elastic:9200/_cat/health?h=st) = 200 ]

Inspired by the above I have created this oneliner:

ESHOST="elastic"
timeout 300 bash -c "until curl --silent --output /dev/null http://$ESHOST:9200/_cat/health?h=st; do printf '.'; sleep 5; done; printf '\n'"