Docker Development - Mistakes 1

Docker Development - Mistakes 1

Hello dear coders

How had you been? I hope you all doing great.
Today I am going to talk about my long (yet very small in total) development using dockerexperiences.
First lets see a simple docker file from my recent hobby project.

FROM golang:alpine
RUN apk update
RUN apk add git

COPY . /go/src
WORKDIR /go/src

RUN set -e \
go get github.com/opentracing/opentracing-go \
&& go get github.com/uber/jaeger-client-go \
&& go get github.com/uber/jaeger-client-go/config

RUN go build -o main .
RUN chmod 755 main
CMD [ "./main" ]

This dockerfile based on golang:alpine and just add git to docker-image.
Then copy current working directory to /go/src
Set working directory and installing opentracing packages.
Finally just build and running main go module.

What is the so called docker mistake here?

Here I didnt notice that, but when every time I run docker-compose up --build after changing the code opentracing and jaeger packages were downloading to docker-image.

I was thinking about it, almost post a question to Stackoverflow asking why my docker always download images

Suddenly I understood my mistake. Its the order in my dockerfile.
What I do is first coping current directory to docker-image and then install necessory packages to image.

What is happening here is that, when there is a change in code docker consider its a fresh new step and all the following commands are executed again as it can not use cached containers.

What I have learned here :

  • Always put package installations at the top of the dockerfile
  • Coping local changes to docker image should be done at the later stage.

I hope this would help someone…
Happy coding…

Written with StackEdit.

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