There was a bug: Docker layers were not cached during build. How did you resolve it, and what was the problem?

The problem with missing Docker layer caching is usually related to Docker being unable to use the cache due to changes in the Dockerfile or build context.

Common reasons:

• The order of instructions in the Dockerfile has changed.
• Using instructions that always change (e.g., ADD with changing files).
• Copying files into the container that change frequently, causing cache invalidation for subsequent layers.
• Using --no-cache during build.

How I solved it:

• Optimized the Dockerfile so that immutable layers come first.
• Minimized the number of changing files copied early on.
• Ensured not to use the --no-cache flag unnecessarily.

Example:

# Bad example
COPY package.json ./
RUN npm install
COPY . ./

# Good example
COPY package.json ./
RUN npm install
COPY . ./

If package.json doesn't change, the layer with npm install is cached, speeding up the build.

Thus, the issue was due to incorrect instruction order and changing files, which prevented layer cache from being used.