How can I wait for a docker container to be up and

问题:

When running a service inside a container, let's say mongodb, the command

docker run -d myimage

will exit instantly, and return the container id. In my CI script, I run a client to test mongodb connection, right after running the mongo container. The problem is: the client can't connect because the service is not up yet. Apart from adding a big sleep 10in my script, I don't see any option to wait for a container to be up and running.

Docker has a command wait which doesn't work in that case, because the container doesn't exist. Is it a limitation of docker? Thanks

回答1:

As commented in a similar issue for docker 1.12

HEALTHCHECK support is merged upstream as per docker/docker#23218 - this can be considered to determine when a container is healthy prior to starting the next in the order

This is available since docker 1.12rc3 (2016-07-14)

docker-compose is in the process of supporting a functionality to wait for specific conditions.

It uses libcompose (so I don't have to rebuild the docker interaction) and adds a bunch of config commands for this. Check it out here: https://github.com/dansteen/controlled-compose

You can use it in Dockerfile like this:

HEALTHCHECK --interval=5m --timeout=3s \
  CMD curl -f http://localhost/ || exit 1

Official docs: https://docs.docker.com/engine/reference/builder/#/healthcheck

回答2:

If you don't want to expose the ports, as is the case if you plan to link the container and might be running multiple instances for testing, then I found this was a good way to do it in one line :) This example is based on waiting for ElasticSearch to be ready:

docker inspect --format '{{ .NetworkSettings.IPAddress }}:9200' elasticsearch | xargs wget --retry-connrefused --tries=5 -q --wait=3 --spider

This requires wget to be available, which is standard on Ubuntu. It will retry 5 times, 3 seconds between tries, even if the connection is refused, and also does not download anything.

回答3:

Found this simple solution, been looking for something better but no luck...

until [ "`/usr/bin/docker inspect -f {{.State.Running}} CONTAINERNAME`"=="true" ]; do
    sleep 0.1;
done;

or if you want to wait until the container is reporting as healthy (assuming you have a healthcheck)

until [ "`/usr/bin/docker inspect -f {{.State.Health.Status}} CONTAINERNAME`"=="healthy" ]; do
    sleep 0.1;
done;

回答4:

If the containerized service you started doesn't necessarily respond well to curl or wget requests (which is quite likely for many services) then you could use nc instead.

Here's a snippet from a host script which starts a Postgres container and waits for it to be available before continuing:

POSTGRES_CONTAINER=`docker run -d --name postgres postgres:9.3`
# Wait for the postgres port to be available
until nc -z $(sudo docker inspect --format='{{.NetworkSettings.IPAddress}}' $POSTGRES_CONTAINER) 5432
do
    echo "waiting for postgres container..."
    sleep 0.5
done

Edit - This example does not require that you EXPOSE the port you are testing, since it accesses the Docker-assigned 'private' IP address for the container. However this only works if the docker host daemon is listening on the loopback (127.x.x.x). If (for example) you are on a Mac and running the boot2docker VM, you will be unable to use this method since you cannot route to the 'private' IP addresses of the containers from your Mac shell.

回答5:

Assuming that you know the host+port of your MongoDB server (either because you used a -link, or because you injected them with -e), you can just use curl to check if the MongoDB server is running and accepting connections.

The following snippet will try to connect every second, until it succeeeds:

#!/bin/sh
while ! curl http://$DB_PORT_27017_TCP_ADDR:$DB_PORT_27017_TCP_PORT/
do
  echo "$(date) - still trying"
  sleep 1
done
echo "$(date) - connected successfully"

回答6:

I've ended up with something like:

#!/bin/bash

attempt=0
while [ $attempt -le 59 ]; do
    attempt=$(( $attempt + 1 ))
    echo "Waiting for server to be up (attempt: $attempt)..."
    result=$(docker logs mongo)
    if grep -q 'waiting for connections on port 27017' <<< $result ; then
      echo "Mongodb is up!"
      break
    fi
    sleep 2
done

回答7:

Throwing my own solution out there:

I'm using docker networks so Mark's netcat trick didn't work for me (no access from the host network), and Erik's idea doesn't work for a postgres container (the container is marked as running even though postgres isn't yet available to connect to). So I'm just attempting to connect to postgres via an ephemeral container in a loop:

#!/bin/bash

docker network create my-network
docker run -d \
    --name postgres \
    --net my-network \
    -e POSTGRES_USER=myuser \
    postgres

# wait for the database to come up
until docker run --rm --net my-network postgres psql -h postgres -U myuser; do
    echo "Waiting for postgres container..."
    sleep 0.5
done

# do stuff with the database...

回答8:

I had to tackle this recetly and came up with an idea. When doing research for this task I got here, so I thought I'd share my solution with future visitors of this post.

Docker-compose-based solution

If you are using docker-compose you can check out my docker synchronization POC. I combined some of the ideas in other questions (thanks for that - upvoted).

The basic idea is that every container in the composite exposes a diagnostic service. Calling this service checks if the required set of ports is open in the container and returns the overall status of the container (WARMUP/RUNNING as per the POC). Each container also has an utility to check upon startup if the dependant services are up and running. Only then the container starts up.

In the example docker-compose environment there are two services server1 and server2 and the client service which waits for both servers to start then sends a request to both of them and exits.

Excerpt from the POC

wait_for_server.sh

#!/bin/bash

server_host=$1
sleep_seconds=5

while true; do
    echo -n "Checking $server_host status... "

    output=$(echo "" | nc $server_host 7070)

    if [ "$output" == "RUNNING" ]
    then
        echo "$server_host is running and ready to process requests."
        break
    fi

    echo "$server_host is warming up. Trying again in $sleep_seconds seconds..."
    sleep $sleep_seconds
done

Waiting for multiple containers:

trap 'kill $(jobs -p)' EXIT

for server in $DEPENDS_ON
do
    /assets/wait_for_server.sh $server &
    wait $!
done

Diagnostic srervice basic implementation (checkports.sh):

#!/bin/bash

for port in $SERVER_PORT; do
    nc -z localhost $port;

    rc=$?

    if [[ $rc != 0 ]]; then
        echo "WARMUP";
        exit;
    fi
done

echo "RUNNING";

Wiring up the diagnostic service to a port:

nc -v -lk -p 7070 -e /assets/checkports.sh

回答9:

test/test_runner

#!/usr/bin/env ruby

$stdout.sync = true

def wait_ready(port)
  until (`netstat -ant | grep #{port}`; $?.success?) do
    sleep 1
    print '.'
  end
end

print 'Running supervisord'
system '/usr/bin/supervisord'

wait_ready(3000)

puts "It's ready :)"

$ docker run -v /tmp/mnt:/mnt myimage ruby mnt/test/test_runner

I'm testing like this whether the port is listening or not. In this case I have test running from inside container, but it's also possible from outside whether mongodb is ready or not.

$ docker run -p 37017:27017 -d myimage

And check whether the port 37017 is listening or not from host container.

回答10:

You can use wait-for-it, "a pure bash script that will wait on the availability of a host and TCP port. It is useful for synchronizing the spin-up of interdependent services, such as linked docker containers. Since it is a pure bash script, it does not have any external dependencies".

However, you should try to design your services to avoid these kind of interdependencies between services. Can your service try to reconnect to the database? Can you let your container just die if it can't connect to the database and let a container orchestrator (e.g. Docker Swarm) do it for you?

回答11:

Docker-compose solution

After docker-compose I dont know name of docker container, so I use

docker inspect -f {{.State.Running}} $(docker-compose ps -q <CONTAINER_NAME>)

and checking true like here https://stackoverflow.com/a/33520390/7438079