Dockerode Sticky Sessions Proof of Concept

This project demonstrates using Dockerode with custom headers to maintain sticky sessions to Docker daemons through HAProxy.

Components

1. Four Docker daemons running in separate containers
2. HAProxy for load balancing and maintaining sticky sessions
3. Node.js client using Dockerode with custom headers

Setup and Running

1. Ensure you have Docker installed on your system.

2. Clone this repository and navigate to the project directory.

3. Build and start the Docker Compose stack:

   docker compose up sut --build

4. The Node.js client will automatically start and attempt to list containers every 5 seconds.

5. You should see in the logs that each client consistently connects to the same Docker daemon.

How it works

• The Node.js client generates a unique client ID and sends it as a custom header (X-Balena-Build-ID) with each request.
• The Node.js client selects a build group, either A or B, and sends it as a custom header (X-Balena-Build-Group) with each request.
• HAProxy uses the build group header to select a backend group, like a subset of Docker daemons.
• HAProxy uses the build ID header to maintain sticky sessions, ensuring that each client always connects to the same Docker daemon.
• You can verify this by checking the logs and seeing that each client ID consistently lists the same server.

Modifying the setup

You can modify the nodejs-client/index.js file to perform different Docker operations or change the frequency of requests. After making changes, rebuild and restart the stack:

docker compose up sut --build

This setup demonstrates that HAProxy can maintain sticky connections between Dockerode clients and Docker daemons based on a custom header.