Heroku Node.js App Fails with 'pnpm: Error: Cannot find matching keyid' After Dyno Restart

Below is some context on Dockerfile design for Node.js apps that might help explain what you’re seeing and why your workaround appears to resolve the issue:

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What Might Have Happened

Changes in a base image (for example, the official Node image) or updates in Build Tooling can sometimes introduce unexpected behavior. Although our Docker documentation doesn’t specifically cover Heroku’s deployment platform or pnpm/corepack updates, here are a couple of general possibilities:

• Upstream Updates: The Node image you are using (in this case, node:20‑alpine) may have recently updated corepack or its configuration. In some cases, when the packaging or signing mechanisms change (for example, involving key handling), you might see errors such as “Cannot find matching keyid.”
• Cache Invalidation and Dependency Management: Docker’s build cache is very useful (as explained in our guides on optimizing Docker builds), and small changes upstream (or in how dependencies are installed) might cause issues when cached layers are suddenly incompatible with new package manager behavior.

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Is the Fix Legitimate?

Your workaround modifies the Dockerfile to disable corepack and then manually install the latest version of pnpm. This approach effectively sidesteps the problem by removing the extra layer of indirection that corepack introduces. In our Dockerfile examples for Node.js applications, we emphasize:

• Layering and Order of Commands: Installing or configuring dependencies early helps ensure that changes only force a rebuild when actual configuration files (like package.json) change.
• Explicit Installation: In several Dockerfile examples in our docs, explicit package manager settings (or commands) are used for clarity and to take advantage of caching (for example as shown in multi‑stage Dockerfiles).

Given this, your change is consistent with best practices by explicitly controlling which version of pnpm is used, and by disabling the tool (corepack) that was causing issues. Still, whenever upstream images change their behavior, it’s a good idea to check:

• The release notes for the base image (node:20‑alpine) to see if there were any changes related to corepack or pnpm.
• Any recent discussions or issues on the upstream tool’s repositories (for example, GitHub issues related to corepack).

If those sources confirm similar issues, then your fix is a sensible and legitimate workaround.

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Summary

• Possible Cause: An upstream update in the Node image or corepack might have introduced changes in how package manager keys are handled, triggering your error during the Docker build.
• Legitimacy of the Fix: Disabling corepack and ensuring you install the latest pnpm aligns with Dockerfile best practices by making dependency installation explicit. This is a commonly recommended approach—in our multi‑stage Dockerfile examples, for instance—to avoid unexpected issues when tooling changes.

For further investigation, keep monitoring the upstream repositories and release notes for Node and corepack, and adjust your Dockerfile as necessary when official guidance is updated.