Advanced docker build technique

Advanced usage of docker build

Usage of Dockerignore#

• Basically, docker build loads all sub directories which cause heavy overhead.
  • If there are lots of sub directories, build needs a lot of time to load all data.
  • We need to ignore unnecessary directories to reduce loading time.
• .dockerignore prevents to load some files and directories.
  • Basically, we can describe original names of files or directories, but it supports some advanced description technique.
  • build means a simple directory name form.
  • */temp* describes directories started with temp inside 1-level sub-directories.
    • For example, log/temp will be ignored from building context.
  • */*/temp* similarly describes directories started with temp inside 2-level sub-directories.
  • temp? means all directories named by 5 characters started with temp.
    • For example, there are tempa , tempb and so on.

# comment
build
*/temp*
*/*/temp*
temp?

Separating building image from production image#

• In Dockerfile script, I have described a way to build an image by Dockerfile.
  • When building docker images, we uses unnecessary packages in production environment.
    • Therefore, we need to remove the redundant files.
  • We can separate production deployment images from build images.
• I have named a building image to build by as build.
  • Similarly, if you need lots of different building environments, you can define multiple environments named by different one.
• In building production image, I could have access to build image by --from={{name}}.
  • At this, I checked that golang:latest image was based on debian:buster, therefore I used the same image for production build.
  • As I’ve mentioned, we can copy files from multiple environments defined in advance.

FROM golang:latest as build

ADD . /workdir

WORKDIR /workdir
RUN go build -o app

FROM debian/buster
WORKDIR /app
COPY --from=build /workdir/app /app/app

CMD ["/app/app"]