Lab #5 : Create an image with ENTRYPOINT instruction
The ENTRYPOINT instruction make your container run as an executable.
ENTRYPOINT can be configured in two forms:
- Exec Form
ENTRYPOINT [“executable”, “param1”, “param2”] - Shell Form
ENTRYPOINT command param1 param2
If an image has an ENTRYPOINT if you pass an argument it, while running container it wont override the existing entrypoint, it will append what you passed with the entrypoint.To override the existing ENTRYPOINT you should user –entrypoint flag when running container.
Pre-requisite:
Tested Infrastructure
| Platform | Number of Instance | Reading Time |
|---|---|---|
| Play with Docker | 1 | 5 min |
Pre-requisite
- Create an account with DockerHub
- Open PWD Platform on your browser
- Click on Add New Instance on the left side of the screen to bring up Alpine OS instance on the right side
Assignment:
- Create an image with ENTRYPOINT instruction(Exec Form)
- ENTRYPOINT instruction in Shell Form
- Override the existing ENTRYPOINT
Create an image with ENTRYPOINT instruction(Exec Form)
Dockerfile
FROM alpine:3.5
LABEL maintainer="Collabnix"
ENTRYPOINT ["/bin/echo", "Hi, your ENTRYPOINT instruction in Exec Form !"]
Build Docker Image
$ docker build -t entrypoint:v1 .
Verify the Image
$ docker image ls
REPOSITORY TAG IMAGE ID CREATED SIZE
entrypoint v1 1d06f06c2062 2 minutes ago 4MB
alpine 3.5 f80194ae2e0c 7 months ago 4MB
Create a container
$ docker container run entrypoint:v1
Hi, your ENTRYPOINT instruction in Exec Form !
ENTRYPOINT instruction in Shell Form
Dockerfile
$ cat Dockerfile
FROM alpine:3.5
LABEL maintainer="Collabnix"
ENTRYPOINT echo "Hi, your ENTRYPOINT instruction in Shell Form !"
Build Docker Image
$ docker build -t entrypoint:v2 .
Verify the Image
$ docker image ls
REPOSITORY TAG IMAGE ID CREATED SIZE
entrypoint v2 cde521f13080 2 minutes ago 4MB
entrypoint v1 1d06f06c2062 5 minutes ago 4MB
alpine 3.5 f80194ae2e0c 7 months ago 4MB
Create a container
$ docker container run entrypoint:v2
Hi, your ENTRYPOINT instruction in Shell Form !
Override the existing ENTRYPOINT
$ docker container run --entrypoint "/bin/echo" entrypoint:v2 "Hello, Welcome to Docker Meetup! "
Hello, Welcome to Docker Meetup!