Show HN: Dynamic load balancing with Docker containers – without swarm mode

Very thorough write-up, looks like a good approach.

A couple of points though:

1) You have a race condition in haproxy.js. If an addNode function is interleaved with a removeNode function, you could have the following result:

  removeNode reads the file
  removeNode replaces the matching line with nothing
  addNode appends a line to the file
  removeNode writes the string to the file

Now, addNode has returned true, but its given server is removed immediately because removeNode is not atomic.

2) in the // Remove Nodes block, why do you only kill the container when `n == rmNodes - 1`. Say you have 2 nodes to remove, this would remove both from the HAProxy config, but only kill the second of the containers, right?