{"id":21696,"date":"2016-05-05T07:28:12","date_gmt":"2016-05-05T12:28:12","guid":{"rendered":"https:\/\/blog.planview.com\/service-startup-and-docker-compose\/"},"modified":"2016-05-05T07:28:12","modified_gmt":"2016-05-05T12:28:12","slug":"service-startup-and-docker-compose","status":"publish","type":"post","link":"https:\/\/blog.planview.com\/service-startup-and-docker-compose\/","title":{"rendered":"Service Startup and Docker Compose"},"content":{"rendered":"
<\/figure>\n

\"Docker\"We make extensive use of Docker and Docker Compose at Tasktop<\/a> for building, testing and deploying our products. One of the pain points that we run in to is services that fail to start when other services are not available – for example a web app that fails to start unless the database is already up and running. Apparently we’re not the only ones<\/a>, so here’s a bit of bash hackery to work around the problem:<\/p>\n

[code lang=text]
\nuntil nc -z -v -w5 $SERVICE_HOST $SERVICE_PORT;
\ndo
\necho "waiting for service to become available on $SERVICE_HOST:$SERVICE_PORT"
\nsleep 1
\ndone
\n[\/code]<\/p>\n

This hack uses netcat (nc) to wait for a socket accepting connections on the specified host and port. The -z<\/code> flag causes netcat to detect the listening socket without actually sending any data.<\/p>\n

To make this work in a Docker container, you’ll have to ensure that netcat is available:<\/p>\n

[code lang=text]
\nRUN apt-get update &&
\napt-get install -y
\nnetcat &&
\napt-get clean &&
\nrm -rf \/var\/lib\/apt\/lists\/*
\n[\/code]<\/p>\n

There are a few down sides to this approach, such as:<\/p>\n