[FIXED] Error 'failed to compute cache key' in Docker Build
The error failed to compute cache key: failed to walk: lstat ...: no such file or directory during docker build occurs when a COPY or ADD instruction in your Dockerfile references a local file or directory that does not exist within the Docker build context.
Quick Diagnostics
.dockerignore filedocker build ensuring proper trailing . context syntaxQuick Solution (1 Minute):
- Verify the source file path exists inside the directory where you run
docker build .- Check if the file is ignored in
.dockerignore.- Specify the root context explicitly when building from subfolders:
docker build -f docker/Dockerfile .
🚀 Step-by-Step Troubleshooting
Step 1: Understand the Docker Build Context
When you execute docker build -t my-image ., the trailing dot . defines the build context. Docker packages and sends files in that directory to the Docker daemon.
If your Dockerfile has:
COPY package.json ./
Targeting a file outside the current working folder will cause failed to compute cache key.
Fix: Move to your project root or adjust your build command context:
docker build -t my-app:latest -f ./docker/Dockerfile .
Step 2: Check .dockerignore Exclusions
Open the .dockerignore file in your root folder. If an ignored rule matches a file targeted by COPY:
src/config.json
Docker excludes it from the context, throwing the failed to compute cache key error.
Fix: Remove the rule or add an exception prefix !:
!src/config.json
Step 3: Check File Case Sensitivity (Linux)
Linux filesystems are case-sensitive. If your file is named App.js but your Dockerfile has:
COPY app.js ./
Docker fails to locate app.js. Update the filename to match exact capitalization.
Prevention Advice
Recommended security practices: