Scenario

You have a container image myapp:dualfix built from /home/interview/Dockerfile that fails during execution.

Task

Identify the issue with image as myapp:dualfix and verify it runs successfully with exit code 0.

Step 1: Try to run the broken image

docker run --rm myapp:dualfix

Should show exec format error, which occurs when trying to execute a binary for a different architecture.

Step 2: Check the binary architecture

docker run --rm myapp:dualfix file /usr/local/bin/app

The file command shows binary architecture. Common mismatch: arm64 (ARM aarch64) binary on amd64 (x86-64) host.

Step 3: Verify host architecture

uname -m

Should show x86_64 (amd64).

Step 4: Examine the Dockerfile and available binaries

cat /home/interview/Dockerfile
ls -l /home/interview/app-*

Identify which binary is being copied and which architecture binaries are available (app-amd64, app-arm64, etc.). The Dockerfile is copying the wrong architecture binary.

Step 5: Fix the Dockerfile

nano /home/interview/Dockerfile

Change the COPY instruction to use the correct architecture binary:

# Before (wrong):
COPY app-arm64 /usr/local/bin/app

# After (correct):
COPY app-amd64 /usr/local/bin/app

Save and exit.

Step 6: Rebuild the image

docker build -t myapp:dualfix .

Step 7: Verify the fix

docker run --rm myapp:dualfix

Should now show x86-64 or amd64 architecture.