Showing posts from February, 2015

How to connect your docker container to a service on the parent host

Recently I needed a docker container to access a service running on the parent host.  A lot of the examples on the internet were very close to what I needed, but not quite. First off, docker's documentation provided an example that (as far as I can see) doesn't actually work.  The following (I think) is meant to inject the src ip address of the parent host's default interface: $ alias hostip="ip route show | grep -Eo 'via \S+' | awk '{ print \$2 }'" $ docker run  --add-host=docker:$(hostip) --rm -it debian What it actually does is inject the ip of the default gateway on the parent host which doesn't help us. Michael Hamrah 's blog details the " gateway approach " of getting the parent's host ip from within the docker container.  This works great, although I wanted to inject the ip on container run and not have that logic within my docker image. Inject the src ip of the docker interface I think the best

How to test for connection leaks

Connection leaks are easy to introduce, hard to spot, can go undetected for a long time and have disastrous consequences. It's not enough to fix a connection leak or code against them, you must write tests that would fail in their presence.  Here I will discuss a number of techniques that could apply to many different languages and frameworks.  I have also provided some concrete examples on github which make use of Dropwizard , JerseyClient and WireMock . What is a connection leak? Each time system A talks to system B over a protocol like http, it requires a TCP/IP connection to send and receive data.  Connections can be re-used for different requests, via a connection pool, or a new connection can be established for each request.  Once system A has finished with the connection, it needs to either return the connection to the pool, or close it.  If this doesn't happen you have a connection leak.   Given a connection leak, everything will continue to work ju