All-Things-Docker-and-Kubernetes

Lab 006: Port Mapping for a Containerized Application

Pre-requisites
Introduction
Create the Files
Build the Image
Dynamically bind the port and Run the Container
Map to a Specific Port and Run the Container
Cleanup

Pre-requisites

Introduction

In this lab, we’ll run a container that serves a basic website written in Go. We’ll get to see how to map the container ports dynamically to ports on the local host. We’ll also get to specify which ports on the local host to bind our container ports to.

Create the Files

Here’s the code for our website.

webapp.go

```go package main import ( "fmt" "net/http" "os" ) func hostHandler(w http.ResponseWriter, r *http.Request) { name, err := os.Hostname() if err != nil { panic(err) } fmt.Fprintf(w, "

HOSTNAME: %s

", name) fmt.Fprintf(w, "

ENVIRONMENT VARS:

") fmt.Fprintf(w, "

") } func rootHandler(w http.ResponseWriter, r *http.Request) { fmt.Fprintf(w, "

Let's do this!

") fmt.Fprintf(w, " Host info
") } func main() { http.HandleFunc("/", rootHandler) http.HandleFunc("/host/", hostHandler) http.ListenAndServe(":8080",nil) } ``` </details> Let's compile and build the packages. ```bash $ env GOARCH=386 GOOS=linux go build webapp.go ``` ```bash $ ll total 6008 drwxrwxr-x 2 ubuntu ubuntu 4096 Jun 23 10:46 ./ drwxr-x--- 9 ubuntu ubuntu 4096 Jun 23 10:34 ../ -rwxrwxr-x 1 ubuntu ubuntu 6137719 Jun 23 10:46 webapp* -rw-rw-r-- 1 ubuntu ubuntu 700 Jun 23 10:44 webapp.go ``` Now let's create the dockerfile. ```bash FROM scratch COPY webapp / EXPOSE 8080 CMD ["/webapp"] ``` ## Build the Image ```bash $ docker build -t "webapp" . ``` ```bash $ docker images REPOSITORY TAG IMAGE ID CREATED SIZE webapp latest 35cc7454ab2d 3 seconds ago 6.14MB ``` ## Dynamically bind the port and Run the Container Run the container in the background using the "-d" flag. To access the website, we should also map the local host's port to a port in the container. Recall that in our dockerfile, our container exposes port 8080. ```bash EXPOSE 8080 ``` To dynamically map the container port to a port on the localhost, use the "-P" flag. In the example below, we see that the container port is binded to port 49153 on the localhost. ```bash $ docker run -d -P webapp ``` ```bash $ docker ps CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES ce03b2560913 webapp "/webapp" 5 seconds ago Up 4 seconds 0.0.0.0:49153->8080/tcp, :::49153->8080/tcp fervent_lichterman ``` Get the IP of your machine. ```bash $ curl ipecho.net/plain; echo ``` Open your web browser and navigate to the IP, followed by the port.

## Map to a Specific Port and Run the Container To specify the port on the localhost to which to bind the container port, use the "-p" flag. ```bash $ docker run -d -p 3000:8080 webapp ``` ```bash $ docker ps CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES e3e1018a9eaa webapp "/webapp" 7 seconds ago Up 6 seconds 0.0.0.0:3000->8080/tcp, :::3000->8080/tcp sad_jemison ce03b2560913 webapp "/webapp" 6 minutes ago Up 6 minutes 0.0.0.0:49153->8080/tcp, :::49153->8080/tcp fervent_lichterman ``` Test it by running a cURL. ```bash $ curl localhost:3000

Let's do this!

Host info
``` If we try to run another container and map to the same local host port, it will throw an error. ```bash $ docker run -d -p 3000:8080 webapp docker: Error response from daemon: driver failed programming external connectivity on endpoint kind_diffie Bind for 0.0.0.0:3000 failed: port is already allocated. ``` ## Cleanup When you're done with the lab, you can stop all running containers by running the command below. ```bash $ docker stop $(docker ps) ``` Once all containers have "Exited" status, remove them. ```bash $ docker ps -a ``` ```bash $ docker container prune -f ``` Finally, remove all images. ```bash $ docker image prune -af ```

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