Had a weird Docker issue today. Image built successfully but ran old code. Turned out to be stale cache layers.

The Problem

# Build succeeds
docker buildx build -t myapp:latest .
# [+] Building 2.3s FINISHED

# But running it shows old behavior!
docker run myapp:latest
# Old code is running??

Changed code, rebuilt image, but the old version still runs.

The Fix

Nuclear option - clear ALL build caches:

# Clear buildx cache
docker buildx prune --all --force

# Clear builder cache
docker builder prune --all --force

# Then rebuild fresh
docker buildx build \
  --platform linux/amd64 \
  -t myapp:latest \
  --load \
  .

This forces a complete rebuild without any cached layers.

Why This Happens

Docker BuildX has multiple cache layers:

1. Build cache (buildx-specific)
2. Builder instance cache
3. Image layer cache

--no-cache only clears #1. BuildX can still reuse #2 and #3, causing stale layers.

My Rebuild Script

#!/bin/bash
# rebuild-fresh.sh

echo "Cleaning caches..."
docker buildx prune --all --force
docker builder prune --all --force

echo "Building..."
docker buildx build \
  --platform linux/amd64 \
  --file Dockerfile \
  --tag myapp:latest \
  --load \
  .

echo "Done!"
docker images myapp:latest

Multi-Platform Builds

For multiple architectures, use --push instead of --load:

docker buildx build \
  --platform linux/amd64,linux/arm64 \
  --tag registry.com/myapp:latest \
  --push \
  .

Can’t use --load with multi-platform (limitation of BuildX).

When to Use This

• Mysterious “old code” in new images
• Build succeeds but behavior is wrong
• After interrupted builds
• When external dependencies update but Dockerfile doesn’t change

Less Nuclear Options

If you don’t want to nuke everything:

# Remove specific builder
docker buildx rm mybuilder
docker buildx create --name mybuilder --use

# Clear old cache only
docker buildx prune --filter "until=168h"  # older than 7 days

# Check what will be deleted
docker buildx du

CI/CD

For GitHub Actions:

- name: Clean build cache
  run: |
    docker buildx prune --all --force

- name: Build
  run: |
    docker buildx build \
      --platform linux/amd64,linux/arm64 \
      --tag $ \
      --push \
      .

Preventing Cache Issues

1. Use .dockerignore

node_modules
.git
*.log
dist

2. Order Dockerfile properly

# Dependencies first (changes less)
COPY package*.json ./
RUN npm ci

# Code last (changes more)
COPY . .
RUN npm run build

3. Explicit cache busting when needed

ARG CACHE_BUST=1
RUN echo "Bust: $CACHE_BUST" && apt-get update

Build with: --build-arg CACHE_BUST=$(date +%s)

Takeaway

When Docker builds behave mysteriously:

1. Prune all caches
2. Rebuild fresh
3. Check .dockerignore

Most “weird Docker issues” are cache-related.