Kubernetes is a popular container orchestration system that lets you automate application deployment, scaling and management tasks via simple command line calls. This guide describes how to build and deploy a simple dockerized web app to a Kubernetes cluster on CentOS 8.<\/p>\n\n\n\n\n\n

1. Testing out containers
2. Building a simple dockerized app using Dockerfile
3. Deploying the app to Kubernetes<\/p>\n\n\n\n

Test hosting on UpCloud!<\/a><\/div>\n<\/div>\n\n\n\n

Testing out containers<\/h2>\n\n\n\n
Let\u2019s start by running a simple docker app to test the container platform.<\/p>\n\n\n\n
1. Run hello-world app with the following command:<\/p>\n\n\n\n
docker run hello-world<\/pre>\n\n\n\n
You should see the app print \u201cHello from Docker!\u201d to your terminal towards the end of the output.<\/p>\n\n\n\n
Running a known container pulls the required image from a public registry and saves it on your docker server.<\/p>\n\n\n\n
2. Check the list of docker images<\/p>\n\n\n\n
docker images<\/pre>\n\n\n\n
After running the hello-world app once, it should show up on the images list.<\/p>\n\n\n\n
REPOSITORY TAG IMAGE ID CREATED SIZE\nhello-world latest fce289e99eb9 15 months ago 1.84kB<\/pre>\n\n\n\n
Now let\u2019s try a more advanced docker app<\/p>\n\n\n\n
1. Run the Ubuntu docker app in interactive mode.<\/p>\n\n\n\n
docker run -it ubuntu bash<\/pre>\n\n\n\n
On success, you\u2019ll be brought directly to Ubuntu prompt.<\/p>\n\n\n\n
2. Test the internet connection from inside docker app by running a command that requires network access.<\/p>\n\n\n\n
On Ubuntu\u2019s terminal prompt, run the following to check it has an internet connection.<\/p>\n\n\n\n
apt update<\/pre>\n\n\n\n
On success, you should see something like the below.<\/p>\n\n\n\n
Get:1 http:\/\/security.ubuntu.com\/ubuntu bionic-security InRelease [88.7 kB]\nGet:2 http:\/\/archive.ubuntu.com\/ubuntu bionic InRelease [242 kB]\n...\nGet:17 http:\/\/archive.ubuntu.com\/ubuntu bionic-backports\/main amd64 Packages [2496 B]\nGet:18 http:\/\/archive.ubuntu.com\/ubuntu bionic-backports\/universe amd64 Packages [4247 B] Fetched 17.7 MB in 5s (3439 kB\/s)<\/pre>\n\n\n\n
Then stop the Ubuntu container with the following command.<\/p>\n\n\n\n
exit<\/pre>\n\n\n\n
In case you cannot access the internet, you might see something similar to the error underneath.<\/p>\n\n\n\n
Err:1 http:\/\/security.ubuntu.com\/ubuntu bionic-security InRelease Temporary failure resolving 'security.ubuntu.com' Err:2 http:\/\/archive.ubuntu.com\/ubuntu<\/a> bionic InRelease Temporary failure resolving 'archive.ubuntu.com' ...<\/pre>\n\n\n\n
To fix this, make sure IP masquerade is enabled at the firewall and then try again.<\/p>\n\n\n\n
firewall-cmd --add-masquerade --permanent\nfirewall-cmd --reload<\/pre>\n\n\n\n
OK, we\u2019ve completed the first part, now let us move on to the next step.<\/p>\n\n\n\n
Building a simple dockerized app using Dockerfile<\/h2>\n\n\n\n
Dockerizing apps is a great way of creating consistent and reliable environments for many tasks regardless of the underlying operating system.<\/p>\n\n\n\n
For this example, we are going to make a simple Golang web server that takes input via the server URL and prints out a hello message.<\/p>\n\n\n\n
1. Start by creating a new directory named \u201cgoserver\u201d<\/p>\n\n\n\n
mkdir goserver<\/pre>\n\n\n\n
2. Create a file named \u201cmain.go\u201d in the goserver directory<\/p>\n\n\n\n
vi goserver\/main.go<\/pre>\n\n\n\n
Enter the following code, then save the file.<\/p>\n\n\n\n
package main\nimport ( \n \"fmt\"\n \"net\/http\"\n)\nfunc main() {\n http.HandleFunc(\"\/\", HelloServer)\n http.ListenAndServe(\":8080\", nil)\n}\nfunc HelloServer(w http.ResponseWriter, r *http.Request) {\n fmt.Fprintf(w, \"Hello, %s!n\", r.URL.Path[1:])\n}<\/pre>\n\n\n\n
3. Create another new file named \u201cDockerfile\u201d with the following command.<\/p>\n\n\n\n
vi Dockerfile<\/pre>\n\n\n\n
Then add the following content to that file, save and exit the text editor.<\/p>\n\n\n\n
FROM golang:alpine as builder\nWORKDIR \/build\nCOPY \/goserver .\nRUN CGO_ENABLED=0 GOOS=linux go build -a -installsuffix cgo -ldflags '-extldflags \"-static\"' -o main .\nFROM scratch\nCOPY --from=builder \/build\/main \/app\/\nWORKDIR \/app\nENV PORT=8080\nCMD [\".\/main\"]<\/pre>\n\n\n\n
4. Next, build a docker image based on our goserver.<\/p>\n\n\n\n
docker build -f Dockerfile -t goserver .<\/pre>\n\n\n\n
5. Additionally, you may wish to clean unused images from the build process.<\/p>\n\n\n\n
docker system prune -f<\/pre>\n\n\n\n
6. Then check that your web app was added to the images list.<\/p>\n\n\n\n
docker images<\/pre>\n\n\n\n
You should see a line such as in the example below.<\/p>\n\n\n\n
REPOSITORY TAG IMAGE ID CREATED SIZE\ngoserver latest 6c0fb70f56fe 55 seconds ago 7.41MB<\/pre>\n\n\n\n
7. Afterwards, test run the web app.<\/p>\n\n\n\n
docker run -d -p 8090:8080 --name goserver goserver<\/pre>\n\n\n\n
8. You can verify that the deployment was successful by checking the running images.<\/p>\n\n\n\n
docker ps -f name=goserver<\/pre>\n\n\n\n
You should see the \u201cgoserver\u201d container running with the status \u201cUp\u201d.<\/p>\n\n\n\n
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES\na16ebdf117b9 goserver \".\/main\" 54 seconds ago Up 53 seconds 0.0.0.0:8090->8080\/tcp goserver<\/pre>\n\n\n\n
Your web app is now reachable both locally and over the internet.<\/p>\n\n\n\n
9. Call it on the command line, for example by using curl with the command below.<\/p>\n\n\n\n
curl http:\/\/localhost:8090\/Joe<\/pre>\n\n\n\n
You should have curl available but if not, install curl using `sudo dnf install curl<\/tt><\/p>\n\n\n\n`
`You can also open the page in your web browser. Replace the public-ip-address<\/span> with the IP of your Master node.<\/p>\n\n\n\n`
`http:\/\/public-ip-address:8090\/Joe<\/tt><\/a><\/p>\n\n\n\n`
`You should see the following response.<\/p>\n\n\n\n`
`Hello, Joe!<\/p>\n\n\n\n`
`12. Once done, stop the web server and remove the image.<\/p>\n\n\n\n`
docker stop goserver && docker rm goserver<\/pre>\n\n\n\nCongratulations, you should now have an idea of what\u2019s included in making simple dockerized apps.<\/p>\n\n\n\nDeploying a dockerized app to Kubernetes<\/h2>\n\n\n\nWe\u2019ve now tested out the container platform and built our own dockerized web app, so the last thing to do is to deploy it on our Kubernetes cluster.<\/p>\n\n\n\nThis part is referring to the Kubernetes configuration installed in our previous tutorial<\/a>.<\/p>\n\n\n\n 1. Create the following configuration file on the master node<\/strong>. Replace the <master_private_IP><\/span> with the private IP address of your master node.<\/p>\n\n\n\n cat > \/etc\/docker\/daemon.json <<EOF\n{\n \"log-driver\": \"json-file\",\n \"log-opts\": {\n \"max-size\": \"100m\"\n },\n \"storage-driver\": \"overlay2\",\n \"storage-opts\": [\n \"overlay2.override_kernel_check=true\"\n ],\n \"insecure-registries\": [ \"<master_private_IP><\/span>:5000\" ]\n}\nEOF<\/pre>\n\n\n\n2. Add the exception for the registry also on all worker nodes<\/strong>. Again, replace the <master_private_IP><\/span> with the private IP address of your master node.<\/p>\n\n\n\ncat > \/etc\/docker\/daemon.json <<EOF\n{\n \"insecure-registries\": [ \"<master_private_IP><\/span>:5000\" ]\n}\nEOF<\/pre>\n\n\n\nThen restart Docker on all nodes<\/strong>.<\/p>\n\n\n\nsystemctl restart docker<\/pre>\n\n\n\nContinue with the rest of the steps on the master node only<\/strong>.<\/p>\n\n\n\n We are going to be using a private registry container for storing and distributing our dockerized app in our cluster.<\/p>\n\n\n\n 3. Get the latest version of the docker registry.<\/p>\n\n\n\ndocker pull registry:2<\/pre>\n\n\n\n4. Run the docker registry on port 5000 using the master node\u2019s private IP address. Replace the <master_private_IP><\/span> with the correct address.<\/p>\n\n\n\ndocker run -dit --restart=always -p <master_private_IP><\/span>:5000:5000 --name registry -e REGISTRY_STORAGE_DELETE_ENABLED=true registry:2<\/pre>\n\n\n\n5. Next, create a deployment artefact for our \u201cgoserver\u201d app.<\/p>\n\n\n\n Please be aware that indentation matters. This artefact is using two spaces for indentation.<\/p>\n\n\n\nvi deployment.yaml<\/pre>\n\n\n\nEnter the following content and again replace the <master_private_IP><\/span> with the correct address.<\/p>\n\n\n\napiVersion: apps\/v1\nkind: Deployment\nmetadata:\n name: goserver\nspec:\n selector:\n matchLabels:\n app: goserver\n replicas: 2\n revisionHistoryLimit: 0\n progressDeadlineSeconds: 30\n strategy:\n type: RollingUpdate\n rollingUpdate:\n maxSurge: 2\n maxUnavailable: 2\n template:\n metadata:\n labels:\n app: goserver\n spec:\n containers:\n - name: goserver\n image: <master_private_IP><\/span>:5000\/goserver:v1\n ports:\n - hostPort: 8090\n containerPort: 8080\n\n---\napiVersion: v1\nkind: Service\nmetadata:\n labels:\n app: goserver\n name: goserver\nspec:\n selector:\n app: goserver\n ports:\n - protocol: TCP\n port: 8090\n targetPort: 8080\n type: ClusterIP<\/pre>\n\n\n\n6. Tag the docker app to add the private registry address and port. As before, replace the <master_private_IP><\/span> with the private IP address of your master node.<\/p>\n\n\n\ndocker tag goserver:latest <master_private_IP><\/span>:5000\/goserver:v1<\/pre>\n\n\n\n7. Then check to make sure the tagged app was created.<\/p>\n\n\n\ndocker images<\/pre>\n\n\n\nIt should show up on the list.<\/p>\n\n\n\n 8. Push the tagged app to the private registry so it can be pulled by Kubernetes deployment. Again, replace the <master_private_IP><\/span> with the private IP address of your master node.<\/p>\n\n\n\n docker push <master_private_IP><\/span>:5000\/goserver:v1<\/pre>\n\n\n\n9. Check that the tagged app was successfully pushed to the registry by querying the registry. Replace the <master_private_IP><\/span> with the private IP address of your master node.<\/p>\n\n\n\n curl -s -X GET http:\/\/<master_private_IP><\/span>:5000\/v2\/goserver\/tags\/list<\/pre>\n\n\n\n{\"name\":\"goserver\",\"tags\":[\"v1\"]}<\/pre>\n\n\n\nNow that we have set up our private repository and pushed the docker image to it, it can be used to deploy the app onto our Kubernetes cluster.<\/p>\n\n\n\n 10. Deploy our goserver using the command below.<\/p>\n\n\n\n kubectl apply -f deployment.yaml<\/pre>\n\n\n\n11. Check that the deployment rollout succeeded.<\/p>\n\n\n\n kubectl rollout status deployment\/goserver<\/pre>\n\n\n\n12. You can also check that the pods are up and running.<\/p>\n\n\n\n kubectl get pods<\/pre>\n\n\n\n13. You should now be able to access the web server on both master and worker nodes.<\/p>\n\n\n\n curl http:\/\/localhost:8090\/Joe<\/pre>\n\n\n\nOr open browser to :8090\/Joe” target=”_blank” rel=”noopener”>http:\/\/<public-IP-address>:8090\/Joe<\/a><\/p>\n\n\n\n Replace the <public-IP-address> with either the public IP address of your master or worker node.<\/p>\n\n\n\n You should see the familiar greeting.<\/p>\n\n\n\n Hello, Joe!<\/p>\n\n\n\n 14. When you wish to delete the test app, revert the deployment with the following command.<\/p>\n\n\n\n kubectl delete -f deployment.yaml<\/pre>\n\n\n\nDone!<\/p>\n\n\n\n All done!<\/h2>\n\n\n\nWhen you need to update \u201cgoserver\u201d codes, you need to dockerized again. Then you also need to push it to the registry with different tags (e.g. v2).<\/p>\n\n\n\n That\u2019s all folks, happy dockerizing!<\/p>\n","protected":false},"featured_media":14966,"comment_status":"open","ping_status":"closed","template":"","community-category":[113,114],"class_list":["post-24881","tutorial","type-tutorial","status-publish","has-post-thumbnail","hentry","community-category-integrations","community-category-kubernetes"],"acf":[],"_links":{"self":[{"href":"https:\/\/studiogo.tech\/upcloudold\/wp-json\/wp\/v2\/tutorial\/24881","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/studiogo.tech\/upcloudold\/wp-json\/wp\/v2\/tutorial"}],"about":[{"href":"https:\/\/studiogo.tech\/upcloudold\/wp-json\/wp\/v2\/types\/tutorial"}],"replies":[{"embeddable":true,"href":"https:\/\/studiogo.tech\/upcloudold\/wp-json\/wp\/v2\/comments?post=24881"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/studiogo.tech\/upcloudold\/wp-json\/wp\/v2\/media\/14966"}],"wp:attachment":[{"href":"https:\/\/studiogo.tech\/upcloudold\/wp-json\/wp\/v2\/media?parent=24881"}],"wp:term":[{"taxonomy":"community-category","embeddable":true,"href":"https:\/\/studiogo.tech\/upcloudold\/wp-json\/wp\/v2\/community-category?post=24881"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}

Testing out containers<\/h2>\n\n\n\nLet\u2019s start by running a simple docker app to test the container platform.<\/p>\n\n\n\n1. Run hello-world app with the following command:<\/p>\n\n\n\n

Deploying a dockerized app to Kubernetes<\/h2>\n\n\n\nWe\u2019ve now tested out the container platform and built our own dockerized web app, so the last thing to do is to deploy it on our Kubernetes cluster.<\/p>\n\n\n\n