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17_setting_envvars.md

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Setting Environment Variables

Docker Documentation References:

Dockerfile

docker build

docker run

docker images

docker rmi

Intent

The purpose of this kata is to familiarize yourself with the process of setting an environment variable within the Dockerfile.

Overview

In this exercise, we will create a simple Dockerfile and set an environment variable with will impact the output of the application. We will then delete the image.

Kata Steps

Create a Dockerfile

Use and editor to create a file named sh_hello_user_Dockerfile, or copy the sh_hello_user_Dockerfile from this repository.

The file should contain the following

FROM alpine:3.6
MAINTAINER [email protected]

ENV DOCKER_USER_NAME Timmy

ENTRYPOINT [ "sh", "-c", "echo $DOCKER_USER_NAME" ]

Build the Image

Command

docker build -f sh_hello_user_Dockerfile .

Output

thought:DockerKata rich$ docker build -f sh_hello_user_Dockerfile .
Sending build context to Docker daemon 428.5 kB
Step 1/4 : FROM alpine:3.6
 ---> a41a7446062d
Step 2/4 : MAINTAINER [email protected]
 ---> Running in c8a1f43cd26a
 ---> a2e52da4f0f7
Removing intermediate container c8a1f43cd26a
Step 3/4 : ENV DOCKER_USER_NAME Timmy
 ---> Running in c4070af347b5
 ---> ad7801c15908
Removing intermediate container c4070af347b5
Step 4/4 : ENTRYPOINT sh -c echo $DOCKER_USER_NAME
 ---> Running in 9c6bec933243
 ---> dd175670ab16
Removing intermediate container 9c6bec933243
Successfully built dd175670ab16

List Images

Command

docker images

Output

thought:DockerKata rich$ docker images
REPOSITORY                                   TAG                 IMAGE ID            CREATED             SIZE
<none>                                       <none>              dd175670ab16        3 seconds ago       3.97 MB

Note: We will use the IMAGE ID which will differ from machine to machine, so you must select what is on your computer for the next two steps.

Run the Image

Command

docker run dd175670ab16

Output

thought:DockerKata rich$ docker run dd175670ab16
Timmy

Delete the Image (and related container)

Command

docker rmi -f dd175670ab16

Output

thought:DockerKata rich$ docker rmi -f dd175670ab16
Deleted: sha256:dd175670ab1602e0c5efd8325a1b7969b24d4c38a629b5615010bf6c721d0209
Deleted: sha256:ad7801c15908ecfe9c15d6a5f37d8acd14e726c6222088c2c110cb5d62a3a20c
Deleted: sha256:a2e52da4f0f75fd2c2f78d202ffeed9bee8ede516fe31ed3af9253490b12dc3e

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