kompose (Derived from the amalgamation of Kubernetes and docker-compose names) is a tool to help users familiar with docker-compose move to Kubernetes. It takes a Docker Compose file and translates it into Kubernetes resources (deployments, services, etc). This guide will demonstrate how one migrate Docker Compose Applications to Kubernetes With Kompose.
Super cool Features of Kompose
- Simplify your development process with Docker Compose and then deploy your containers to a production cluster
- Convert your
docker-compose.yamlwith one simple command kompose convert - Immediately bring up your cluster with
kompose up - Bring it back down with
kompose down
What is needed before we begin
Before we proceed with the guide, we assume you have a Kubernetes cluster, and the kubectl command-line tool already configured to communicate with your cluster. If these requirements are not met, you can set up a simple single node Kubernetes cluster using minikube by following the guide below. If you are ready to proceed, continue to install kompose.
Install Minikube Kubernetes on CentOS 8 / CentOS 7 with KVM
Step 1: Getting Kompose Installed on Linux, macOS
Download the latest binary release of Kompose. You can check Kompose Github Page for release versions.
--- Linux ---
curl -s https://api.github.com/repos/kubernetes/kompose/releases/latest | grep browser_download_url | grep linux-amd64 | cut -d '"' -f 4 | wget -qi -
mv kompose-linux-amd64 kompose
--- macOS ---
curl -s https://api.github.com/repos/kubernetes/kompose/releases/latest | grep browser_download_url | grep darwin-amd64 | cut -d '"' -f 4 | wget -qi -
mv kompose-darwin-amd64 komposeMake the binary file executable and move it to the /usr/local/bin directory.
chmod x kompose
sudo mv ./kompose /usr/local/bin/komposeCheck version once installed:
$ kompose version
1.21.0 (992df58d8)Step 2: Create a sample image from Dockerfile
We are going to create Nginx reverse proxy that proxies requests to an apache container
Create a file named Dockerfile and add the contents below.
cat > Dockerfile<<EOF
# Sample Dockerfile for Kompose
FROM nginx:alpine
COPY nginx.conf /etc/nginx/conf.d/default.conf
EXPOSE 8081
EOFAnd this is the config file (nginx.conf) we are copying into the image
cat >nginx.conf<<EOF
upstream apache-container {
server 0.0.0.0:80;
}
server {
listen 8081;
location / {
proxy_pass http://apache-container;
proxy_redirect off;
proxy_set_header Host $host;
proxy_set_header X-Real-IP $remote_addr;
proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
proxy_set_header X-Forwarded-Host $server_name;
}
}
EOFIt is a simple reverse proxy listening for requests at port 8081 then routes the traffic to the upstream server listening at port 80.
Step 3: Build a container image
Open a terminal in your project and type the following command to build our image using podman
$ podman build -t reverseproxy:v1 .
STEP 1: FROM nginx:alpine
Getting image source signatures
Copying blob cbdbe7a5bc2a done
Copying blob c554c602ff32 done
Copying config 89ec9da682 done
Writing manifest to image destination
Storing signatures
STEP 2: COPY nginx.conf /etc/nginx/conf.d/default.conf
--> d86b4e89749
STEP 3: EXPOSE 8081
STEP 4: COMMIT reverseproxy:v1
--> b00d80e0056
b00d80e00560c205e0580d4b751b1a67da7e77e7fc73803b006ff10389bb4732
-- With Docker ---
$ docker build -t reverseproxy:v1 .After the image has been built, we should be able to see it as follows
$ podman images
REPOSITORY TAG IMAGE ID CREATED SIZE
localhost/reverseproxy v1 b00d80e00560 19 seconds ago 21.2 MBStep 3: Push Container image to Image registry
You can push the image to any of the public registries or even to one you have created/private.
This example used Docker Hub image registry.
$ podman tag docker.io//reverseproxy:v1
Example:
$ podman tag localhost/reverseproxy:v1 docker.io/penchant/reverseproxy:v1Authenticate to your Image registry – for me this is docker.io
$ podman login docker.io
Username:
Password:
Login Succeeded!Once logged in, push the image, example:
$ podman push docker.io/penchant/reverseproxy:v1
Getting image source signatures
Copying blob 113ce2720837 done
Copying blob 3810cc0c140f done
Copying blob 3e207b409db3 done
Copying config b00d80e005 done
Writing manifest to image destination
Storing signaturesYou can find more about pushing and pulling of images from DockerHub using this guide:
Publish Container Images to Docker Hub / Image registry with Podman
Step 4: Create a docker-compose.yaml
This is a file that Docker Compose would use to create services and run a multi-container environment for our sample project. Notice the image we are using is the one we have just built and pushed to DockerHub
$ vim docker-compose.yaml
version: "3"
services:
reverseproxy:
image: docker.io/penchant/reverseproxy:v1
ports:
- 8081:8081
restart: always
apache:
depends_on:
- reverseproxy
image: httpd:alpine
restart: alwaysAfter our docker-compose.yaml file is spick and span, there are two options we can exploit while running the project via kompose. First, we can convert the docker-compose.yaml file to separate yaml files such as deployment, service and persistentvolumeclaim then use kubectl to apply them or we can simply use one kompose up command to do the magic. Since I would wish to examine the separate files, we are going to convert first as follows:
$ kompose convert
INFO Kubernetes file "reverseproxy-service.yaml" created
INFO Kubernetes file "apache-deployment.yaml" created
INFO Kubernetes file "reverseproxy-deployment.yaml" createdNow we have three yaml files created with names that explain what they do. One is a service, the other are a deployments.
We can proceed to apply these files using kubectl as illustrated below
$ kubectl apply -f reverseproxy-service.yaml,apache-deployment.yaml,reverseproxy-deployment.yaml
service/reverseproxy created
deployment.apps/apache created
deployment.apps/reverseproxy createdCheck the service, pods, and deployments
$ kubectl get deployment,svc,pods
NAME READY UP-TO-DATE AVAILABLE AGE
deployment.apps/apache 1/1 1 1 113m
deployment.apps/reverseproxy 1/1 1 1 105m
NAME TYPE CLUSTER-IP EXTERNAL-IP PORT(S) AGE
service/kubernetes ClusterIP 10.96.0.1 443/TCP 122m
service/reverseproxy ClusterIP 10.97.210.141 8081/TCP 113m
NAME READY STATUS RESTARTS AGE
pod/apache-7945cd6844-5hpf8 1/1 Running 0 113m
pod/reverseproxy-8646fb7c4f-j6742 1/1 Running 0 105mAs you can see, even before the respective yaml files are fine-tuned to befit specific configurations, they were able to launch kubernetes resources.
Note:
You can change details in the yaml files derived after kompose acts upon Docker-Compose files to your specific needs. The good thing is that kompose does most of the heavy-lifting and you can simply add what you need to add.
Kompose is a brilliant tool and can get you from absolutely nothing to a working Kubernetes application. Try it out in your projects to see the power that you can take advantage of by leveraging on what has been developed in kompose for you.
If you are quite the explorer, find other guides below for your conquest:
How To run Docker Containers using Podman and Libpod
How To Manually Pull Container images used by Kubernetes kubeadm
Top Minimal Container Operating Systems for running Kubernetes
Add Harbor Image Registry Pull Secret to Kubernetes / OpenShift
Configure Active Directory (AD) Authentication for Harbor Registry
