All-Things-Docker-and-Kubernetes

Lab 002: Creating the Dockerfile and the Image

• Pre-requisites
• Introduction
• Create the Files
• Build the Image
• Run the container
• Cleanup

Pre-requisites

• Install Docker
• Install Go

Introduction

In this lab, we’ll run a lightweight container that runs a custom package.

Create the Files

Here’s a custom hello-world.go binary. This is the same code that was used in the pre-requisite section.

// Hello Word in Go by Vivek Gite
package main
 
// Import OS and fmt packages
import ( 
	"fmt" 
	"os" 
)
 
// Let us start
func main() {
    fmt.Println("Hello, world!")  // Print simple text on screen
    fmt.Println(os.Getenv("USER"), ", Let's be friends!") // Read Linux $USER environment variable 
} 

If you haven’t build and compiled yet, please do so.

$ go run hello-world.go 
$ go build hello-world.go
$ ls -l hello*
$ ./hello-world

Let’s now create the dockerfile.

FROM scratch
COPY hello-world /
CMD ["/hello-world"]

A Few Notes on the dockerfile

• The FROM line specifies the base image tha we’ll use. Here we’re using a very minal image called “scratch”.
• COPY copies the hello-world files from our host onto a layer of the image.
• Finally, the CMD tells the container the default command to run when the container is launched.

Build the Image

Use the build command, followed by the directory where the dockerfile is.

$ docker build .

Sending build context to Docker daemon   1.77MB
Step 1/3 : FROM scratch
 --->
Step 2/3 : COPY hello-world /
 ---> ace21a3aa6c1
Step 3/3 : CMD ["/hello-world"]
 ---> Running in f9d66d34a3ee
Removing intermediate container f9d66d34a3ee
 ---> 937c8df2598b
Successfully built 937c8df2598b 

Checking the docker images, we see that the image was created without a repo name and tag.

$ docker images

REPOSITORY   TAG       IMAGE ID       CREATED          SIZE
<none>       <none>    937c8df2598b   46 seconds ago   1.77MB 

To remove the image, run the command below. Make sure to add the image ID at the end. We don’t need to specify the entire image ID.

$ docker rmi 937 

Let’s create the image again, but this time let’s add a tag.

$ docker build . -t my-hello-world

Sending build context to Docker daemon   1.77MB
Step 1/3 : FROM scratch
 --->
Step 2/3 : COPY hello-world /
 ---> b540b27e4866
Step 3/3 : CMD ["/hello-world"]
 ---> Running in 31c09c3a4794
Removing intermediate container 31c09c3a4794
 ---> 5635489bb18b
Successfully built 5635489bb18b
Successfully tagged my-hello-world:latest 

Verify.

$ docker images

REPOSITORY       TAG       IMAGE ID       CREATED              SIZE
my-hello-world   latest    5635489bb18b   About a minute ago   1.77MB 

Run the container

$ docker run my-hello-world

Hello, world!
Let's be friends! 

The container will run the binary and then exit out. If we check the list of running containers,

$ docker ps
CONTAINER ID   IMAGE     COMMAND   CREATED   STATUS    PORTS     NAMES 

$ docker ps -a
CONTAINER ID   IMAGE            COMMAND          CREATED              STATUS                          PORTS     NAMES
05d5dad77d2c   my-hello-world   "/hello-world"   About a minute ago   Exited (0) About a minute ago             wonderful_rhodes 

Cleanup

When you’re done with the lab, you can stop all running containers by running the command below.

$ docker stop $(docker ps) 

Once all containers have “Exited” status, remove them.

$ docker ps  -a 

$ docker container prune -f 

Finally, remove all images.

$ docker image prune -af 

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