AWS CLI and Mercurial: Automating Legacy Code Deployment to AWS

I watched my deploy fail for the third time that morning. The culprit wasn’t AWS. It wasn’t the network. It was a single, outdated Mercurial repo buried deep in a build pipeline no one had touched in years.

If you’ve ever worked with AWS CLI, you know it’s built to move fast. It speaks in commands, not ceremony. Mercurial, on the other hand, is a veteran—older than Git, still running in corners of production where change feels risky. Getting these two to work together isn’t about nostalgia. It’s about control. It’s about keeping what works, and making it work better.

AWS CLI and Mercurial: The Core Setup

To connect AWS CLI with Mercurial, the first step is authentication. AWS CLI needs valid credentials, usually set through aws configure or environment variables. Mercurial needs no more than a clean local copy of the repository. The trick is in the bridge. You’ll need build scripts—or better, CI/CD pipelines—that can pull Mercurial sources, run AWS CLI commands, and deliver artifacts to S3, CodeDeploy, or any AWS service you choose.

For a typical setup:

1. Install AWS CLI v2. Ensure your IAM user has the right permissions.
2. Install Mercurial (hg) on your build environment.
3. Pull the code from your Mercurial repo:

hg clone https://your-hg-repo

1. Run your build or packaging steps.
2. Push to AWS:

aws s3 cp ./build/ s3://your-bucket-name --recursive

The key is automation. Once you script this flow, you can run it on any machine, in any region. Your builds won’t care if the code came from GitHub, Bitbucket, or a dusty server in the corner—if Mercurial can pull it, AWS CLI can ship it.

Why Keep Mercurial Alive?

Legacy codebases often hold production-critical logic. Migrating them to Git is possible but risky when deadlines are tight. AWS CLI allows teams to keep Mercurial repositories alive in production pipelines without forcing a massive migration. This is especially valuable for regulated environments where change control is a factor.

Scaling the Workflow

As workloads grow, so do the risks of manual steps. Integrating AWS CLI and Mercurial into a single automated pipeline means you can scale deployments without scaling the human error rate. TAGs in Mercurial map cleanly to versioned S3 paths, making rollbacks instant. AWS CLI’s filters and sync options let you deploy only what changes, saving bandwidth and time.

Security and Access Control

Lock down your AWS credentials. Use IAM roles when possible, especially in EC2 or containerized build agents. For Mercurial, limit repo access to read-only for build users. In CI/CD systems, store secrets in secure variables and never hard-code them in scripts.

The Fast Path to Production

Every pipeline should aim for this: commit, build, deploy—fast, predictable, no drama. By combining AWS CLI’s speed with Mercurial’s stability, you get exactly that. Once it’s wired up, deployments move in minutes, and downtime becomes rare.

If you want to see this kind of workflow in action without weeks of setup, you can spin it up right now. Go to hoop.dev and watch it run live in minutes—AWS CLI, Mercurial, and automation all in one tight loop.