Multi-stage builds in Docker are powerful, enabling streamlined images and optimized build processes by allowing each FROM statement to start with a fresh layer. However, a known limitation is the inability to natively share environment variables between stages. Environment variables set in one stage aren’t directly accessible in subsequent stages due to Docker’s isolation design for layers.

To transfer environment variables, developers use workarounds like writing variables to a file and copying it to subsequent stages. For example:

dockerfile
# First Stage
FROM base-image AS stage1
RUN echo "MY_VAR=$MY_VAR" > /env_vars

# Second Stage
FROM final-image
COPY --from=stage1 /env_vars /env_vars
RUN export $(cat /env_vars)

This approach reads from a file to replicate environment variables, providing a way to reuse configuration across stages despite Docker’s isolation boundaries.