ConPod.md

Container

• the container only lives as long as the process inside it is alive

How to run a container ?

docker run ubuntu

• docker starts a container using ubuntu image that has CMD ["bash"] as "running process"
• bash is a shell that listens for input from terminal , in our case bash doenst find a terminal and it exits

How to specify a different command ?

docker run ubuntu sleep 5

• container will sleep 5 sec and will exit

How to specify a different command permanently?

• create a new Dockerfile

FROM ubuntu
CMD sleep 5
or 
CMD ["sleep", "5"] # command and arg should be separate elements of the list

• build the image

docker build -t myubuntu .

• run container

docker run myubuntu

• container will sleep 5 sec and will exit

What if you want to sleep 10 ?

docker run myubuntu sleep 10

Better option ?

• create Dockerfile and use ENTRYPOINT

FROM ubuntu
ENTRYPOINT ["sleep"]

• run the container by passing only the arg (10) to the starting process (ENTRYPOINT - sleep in our case)

docker run myubuntu 10

• if you dont specify 10 from command will errror, solution is next

---

CMD - command line parameter will get replaced entirely

ENTRYPOINT - command line parameter will get appended

---

• the best of both worlds:

FROM ubuntu
ENTRYPOINT ["sleep"]
CMD ["5"]

• if run docker run myubuntu - sleep 5

• if run docker run myubuntu 10 - sleep 10

• ENTRYPOINT doesnt change , but the argument changes

• to overwrite entrypoint

docker run --entrypoint sleep2.0 myubuntu 10 (assuming sleep2.0 is valid command)

• this will execute sleep2.0 10 and exit

---

Pod

cat ubuntu-pod.yaml

apiVersion: v1
kind: Pod
metadata:
  name: ubuntu
spec:
  containers:
  - name: ubuntu
    image: myubuntu
    command: ["sleep2.0"]
    args: ["10"]

Container            -------  Pod

ENTRYPOINT ["sleep"] -------  command: ["sleep2.0"]    (overwrites)
CMD        ["5"]     -------  args:    ["10"]          (overwrites)