Dockerizing a Next.js Application: Lessons Learned

What we did: Initial Dockerfile: We started with a basic Dockerfile that was designed to work with a Next.js project: Used the official Node.js 18 Alpine image as the base. Set the working directory to /app. Copied the package.json and pnpm-lock.yaml files into the container. Installed pnpm globally. Ran pnpm install to install the project dependencies. Copied the next.config.js file and the rest of the application code. Built the Next.js application using pnpm run build. Set the command to start the Next.js server using pnpm start. Encountered the "pnpm: not found" error: When trying to build the Docker image, we encountered an error where pnpm was not found. This was because we had not installed pnpm globally in the Docker container. Resolved the "pnpm: not found" error: To fix this, we updated the Dockerfile to include a step to install pnpm globally using npm install -g pnpm before running pnpm install. Verified the build process: After making the changes, we were able to successfully build the Docker image and run the Next.js application inside the container. What we learned: Importance of matching Node.js versions: We initially used the Node.js 14 Alpine image, but this was not compatible with the version of pnpm required by the project. We had to update the base image to Node.js 18 to resolve this issue. Copying project files into the Docker container: We learned that it's important to copy the necessary project files (like package.json, pnpm-lock.yaml, and next.config.js) into the Docker container before running the build and install commands. Handling global dependencies: We discovered that we needed to install pnpm globally in the Docker container to ensure it was available for the pnpm install and pnpm run build commands. Importance of updating the Dockerfile when dependencies change: We discussed the need to update the Dockerfile whenever new dependencies are added to the project, to ensure the Docker image includes the latest dependencies. Errors encountered and how we resolved them: "pnpm: not found" error: This error occurred because we had not installed pnpm globally in the Docker container. We resolved this by adding the RUN npm install -g pnpm step to the Dockerfile. No package.json found error: This error occurred because we were not copying the package.json file into the Docker container before running pnpm install. We fixed this by adding a COPY package.json pnpm-lock.yaml ./ step to the Dockerfile. Overall, we went through the process of creating a Dockerfile for a Next.js project, encountered and resolved a few issues, and learned about the importance of matching Node.js versions, copying project files, handling global dependencies, and updating the Dockerfile when dependencies change.