Working with database

In this chapter, we will deploy a database, configure our application to use it, and set up automatic DB migrations and initializations.

The application described in this chapter is not intended for use in production environments as-is. Note that successful completion of this entire guide is required to create a production-ready application.

Preparing the environment

If you haven’t prepared your environment during previous steps, please, do it using the instructions provided in the “Preparing the environment” chapter.

If your environment has stopped working or instructions in this chapter don’t work, please, refer to these hints:

docker run hello-world

Unable to find image 'hello-world:latest' locally
latest: Pulling from library/hello-world
b8dfde127a29: Pull complete
Digest: sha256:9f6ad537c5132bcce57f7a0a20e317228d382c3cd61edae14650eec68b2b345c
Status: Downloaded newer image for hello-world:latest

Hello from Docker!
This message shows that your installation appears to be working correctly.

docker run hello-world

Unable to find image 'hello-world:latest' locally
latest: Pulling from library/hello-world
b8dfde127a29: Pull complete
Digest: sha256:9f6ad537c5132bcce57f7a0a20e317228d382c3cd61edae14650eec68b2b345c
Status: Downloaded newer image for hello-world:latest

Hello from Docker!
This message shows that your installation appears to be working correctly.

sudo systemctl restart docker

sudo systemctl status docker

● docker.service - Docker Application Container Engine
     Loaded: loaded (/lib/systemd/system/docker.service; enabled; vendor preset: enabled)
     Active: active (running) since Thu 2021-06-24 13:05:17 MSK; 13s ago
TriggeredBy: ● docker.socket
       Docs: https://docs.docker.com
   Main PID: 2013888 (dockerd)
      Tasks: 36
     Memory: 100.3M
     CGroup: /system.slice/docker.service
             └─2013888 /usr/bin/dockerd -H fd:// --containerd=/run/containerd/containerd.sock

dockerd[2013888]: time="2021-06-24T13:05:16.936197880+03:00" level=warning msg="Your kernel does not support CPU realtime scheduler"
dockerd[2013888]: time="2021-06-24T13:05:16.936219851+03:00" level=warning msg="Your kernel does not support cgroup blkio weight"
dockerd[2013888]: time="2021-06-24T13:05:16.936224976+03:00" level=warning msg="Your kernel does not support cgroup blkio weight_device"
dockerd[2013888]: time="2021-06-24T13:05:16.936311001+03:00" level=info msg="Loading containers: start."
dockerd[2013888]: time="2021-06-24T13:05:17.119938367+03:00" level=info msg="Loading containers: done."
dockerd[2013888]: time="2021-06-24T13:05:17.134054120+03:00" level=info msg="Daemon has completed initialization"
systemd[1]: Started Docker Application Container Engine.
dockerd[2013888]: time="2021-06-24T13:05:17.148493957+03:00" level=info msg="API listen on /run/docker.sock"

docker run hello-world

Unable to find image 'hello-world:latest' locally
latest: Pulling from library/hello-world
b8dfde127a29: Pull complete
Digest: sha256:9f6ad537c5132bcce57f7a0a20e317228d382c3cd61edae14650eec68b2b345c
Status: Downloaded newer image for hello-world:latest

Hello from Docker!
This message shows that your installation appears to be working correctly.

minikube start

kubectl config set-context minikube --namespace=werf-guide-app

😄  minikube v1.20.0 on Ubuntu 20.04
✨  Using the docker driver based on existing profile
👍  Starting control plane node minikube in cluster minikube
🚜  Pulling base image ...
🎉  minikube 1.21.0 is available! Download it: https://github.com/kubernetes/minikube/releases/tag/v1.21.0
💡  To disable this notice, run: 'minikube config set WantUpdateNotification false'

🔄  Restarting existing docker container for "minikube" ...
🐳  Preparing Kubernetes v1.20.2 on Docker 20.10.6 ...
🔎  Verifying Kubernetes components...
    ▪ Using image gcr.io/google_containers/kube-registry-proxy:0.4
    ▪ Using image k8s.gcr.io/ingress-nginx/controller:v0.44.0
    ▪ Using image registry:2.7.1
    ▪ Using image docker.io/jettech/kube-webhook-certgen:v1.5.1
    ▪ Using image docker.io/jettech/kube-webhook-certgen:v1.5.1
    ▪ Using image gcr.io/k8s-minikube/storage-provisioner:v5
🔎  Verifying registry addon...
🔎  Verifying ingress addon...
🌟  Enabled addons: storage-provisioner, registry, default-storageclass, ingress
🏄  Done! kubectl is now configured to use "minikube" cluster and "werf-guide-app" namespace by default

Restarting existing docker container for "minikube"

minikube tunnel --cleanup=true

minikube start --namespace werf-guide-app

kubectl config set-context minikube --namespace=werf-guide-app

😄  minikube v1.20.0 on Ubuntu 20.04
✨  Using the docker driver based on existing profile
👍  Starting control plane node minikube in cluster minikube
🚜  Pulling base image ...
🎉  minikube 1.21.0 is available! Download it: https://github.com/kubernetes/minikube/releases/tag/v1.21.0
💡  To disable this notice, run: 'minikube config set WantUpdateNotification false'

🔄  Restarting existing docker container for "minikube" ...
🐳  Preparing Kubernetes v1.20.2 on Docker 20.10.6 ...
🔎  Verifying Kubernetes components...
    ▪ Using image gcr.io/google_containers/kube-registry-proxy:0.4
    ▪ Using image k8s.gcr.io/ingress-nginx/controller:v0.44.0
    ▪ Using image registry:2.7.1
    ▪ Using image docker.io/jettech/kube-webhook-certgen:v1.5.1
    ▪ Using image docker.io/jettech/kube-webhook-certgen:v1.5.1
    ▪ Using image gcr.io/k8s-minikube/storage-provisioner:v5
🔎  Verifying registry addon...
🔎  Verifying ingress addon...
🌟  Enabled addons: storage-provisioner, registry, default-storageclass, ingress
🏄  Done! kubectl is now configured to use "minikube" cluster and "werf-guide-app" namespace by default

Restarting existing docker container for "minikube"

kubectl create namespace werf-guide-app
kubectl create secret docker-registry registrysecret \
  --docker-server='https://index.docker.io/v1/' \
  --docker-username='<Docker Hub username>' \
  --docker-password='<Docker Hub password>'

namespace/werf-guide-app created
secret/registrysecret created

Preparing the repository

cd ~/werf-guide/app

# To see what changes we will make later in this chapter, let's replace all the application files
# in the repository with new, modified files containing the changes described below.
git rm -r .
cp -Recurse -Force ~/werf-guide/guides/examples/java_springboot/040_db/* .
git add .
git commit -m WIP

# Enter the command below to show the files we are going to change.
git show --stat
# Enter the command below to show the changes that will be made.
git show

cd ~/werf-guide/app

# To see what changes we will make later in this chapter, let's replace all the application files
# in the repository with new, modified files containing the changes described below.
git rm -r .
cp -rf ~/werf-guide/guides/examples/java_springboot/040_db/. .
git add .
git commit -m WIP

# Enter the command below to show files we are going to change.
git show --stat
# Enter the command below to show the changes that will be made.
git show

# Clone the example repository to ~/werf-guide/guides (if you have not cloned it yet).
if (-not (Test-Path ~/werf-guide/guides)) {
  git clone https://github.com/werf/website $env:HOMEPATH/werf-guide/guides
}

# Copy the (unchanged) application files to ~/werf-guide/app.
rm -Recurse -Force ~/werf-guide/app
cp -Recurse -Force ~/werf-guide/guides/examples/java_springboot/030_assets ~/werf-guide/app

# Make the ~/werf-guide/app directory a git repository.
cd ~/werf-guide/app
git init
git add .
git commit -m initial

# To see what changes we will make later in this chapter, let's replace all the application files
# in the repository with new, modified files containing the changes described below.
git rm -r .
cp -Recurse -Force ~/werf-guide/guides/examples/java_springboot/040_db/* .
git add .
git commit -m WIP

# Enter the command below to show the files we are going to change.
git show --stat
# Enter the command below to show the changes that will be made.
git show

# Clone the example repository to ~/werf-guide/guides (if you have not cloned it yet).
test -e ~/werf-guide/guides || git clone https://github.com/werf/website ~/werf-guide/guides

# Copy the (unchanged) application files to ~/werf-guide/app.
rm -rf ~/werf-guide/app
cp -rf ~/werf-guide/guides/examples/java_springboot/030_assets ~/werf-guide/app

# Make the ~/werf-guide/app directory a git repository.
cd ~/werf-guide/app
git init
git add .
git commit -m initial

# To see what changes we will make later in this chapter, let's replace all the application files
# in the repository with new, modified files containing the changes described below.
git rm -r .
cp -rf ~/werf-guide/guides/examples/java_springboot/040_db/. .
git add .
git commit -m WIP

# Enter the command below to show files we are going to change.
git show --stat
# Enter the command below to show the changes that will be made.
git show

Making our application stateful

At this point, our application does not use a database and does not store any data (i.e., it is stateless). To make it stateful, we need prepare the application to work with the MySQL database (we will use it to store the application state).

The following changes have been made to our application:

1. Installing dependencies for working with the MySQL database.
2. Configuring access to the database.
3. Adding the database model.
4. Adding routes that use the new model.

New dependencies have been added to the pom.xml configuration file:

...
<dependency>
	<groupId>org.springframework.boot</groupId>
	<artifactId>spring-boot-starter-data-jpa</artifactId>
</dependency>
<dependency>
	<groupId>mysql</groupId>
	<artifactId>mysql-connector-java</artifactId>
	<scope>runtime</scope>
</dependency>

• spring-boot-starter-data-jpa — a starter module for using Spring Data JPA with Hibernate;
• mysql-connector-java — a MySQL connector for Java.

Adding /remember and /say endpoints to the application

Let’s add two new endpoints to our application. The /remember endpoint will store the data to the database while the /say endpoint will retrieve the data from it.

Let’s add a new entity to work with the database:

package io.werf.werfguidesapp.domain;

import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.Table;


@Entity
@Table(name = "talkers")
public class Talker {

	@Id
	@GeneratedValue(strategy = GenerationType.AUTO)
	private Integer id;
	
	@JoinColumn(name = "answer")
	private String answer;
	
	@JoinColumn(name = "name")
	private String name;

	public Integer getId() {
		return id;
	}

	public Talker() {

	}

	public Talker(String answer, String name) {
		this.answer = answer;
		this.name = name;
	}

	public void setId(Integer id) {
		this.id = id;
	}

	public String getAnswer() {
		return answer;
	}

	public void setAnswer(String answer) {
		this.answer = answer;
	}

	public String getName() {
		return name;
	}

	public void setName(String name) {
		this.name = name;
	}
}

Add a CRUD repository to use the database:

package io.werf.werfguidesapp.repos;

import org.springframework.data.repository.CrudRepository;

import io.werf.werfguidesapp.domain.Talker;

public interface TalkersRepo extends CrudRepository<Talker, Integer> {

}

You don’t have to add database migrations thanks to the spring.jpa.hibernate.ddl-auto=update property we set in the application.properties. As a result, Hibernate will automatically generate the database structure during work based on the created entities.

Add a new controller:

package io.werf.werfguidesapp.controllers;

import io.werf.werfguidesapp.domain.Talker;
import io.werf.werfguidesapp.repos.TalkersRepo;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RequestParam;
import org.springframework.web.bind.annotation.RestController;

import java.util.Optional;

@RestController
public class TalkerController {
	
	@Autowired
	private TalkersRepo talkersRepo;

	@GetMapping("/remember")
	public String Remember(@RequestParam String answer, @RequestParam String name) {
		Talker talker = new Talker(answer, name);
		talkersRepo.save(talker);
		return "Got it.\n";
	}
	
	@GetMapping("/say")
	public String Say() {
		Optional<Talker> talker = talkersRepo.findById(1);
		if (talker.isPresent()) {
			return talker.get().getAnswer() + ", " + talker.get().getName() + "\n";
		} else return "I have nothing to say.\n";
	}

}

New endpoints, /remember and /say, are ready.

Deploying a MySQL database and connecting to it

In real life, a database can be a part of the Kubernetes infrastructure or run outside of it. Outside of Kubernetes, you can deploy and maintain a database yourself or use a managed solution like Amazon RDS. For illustrative purposes, let’s deploy a MySQL database inside the Kubernetes cluster using the following basic StatefulSet:

apiVersion: apps/v1
kind: StatefulSet
metadata:
  name: mysql
spec:
  serviceName: mysql
  selector:
    matchLabels:
      app: mysql
  template:
    metadata:
      labels:
        app: mysql
    spec:
      containers:
      - name: mysql
        image: mysql:8
        args: ["--default-authentication-plugin=mysql_native_password"]
        ports:
        - containerPort: 3306
        env:
          - name: MYSQL_DATABASE
            value: werf-guide-app
          - name: MYSQL_ROOT_PASSWORD
            value: password
        volumeMounts:
        - name: mysql-data
          mountPath: /var/lib/mysql
  volumeClaimTemplates:
  - metadata:
      name: mysql-data
    spec:
      accessModes: ["ReadWriteOnce"]
      resources:
        requests:
          storage: "100Mi"

---
apiVersion: v1
kind: Service
metadata:
  name: mysql
spec:
  selector:
    app: mysql
  ports:
  - port: 3306

Note that you can also use a database deployed differently. In this case, you will not need the above StatefulSet, while all further steps remain unchanged.

Now let’s configure our application to use the new database:

spring.jpa.hibernate.ddl-auto=update
spring.datasource.url=jdbc:mysql://${DB_HOST}:3306/${DB_NAME}
spring.datasource.username=${DB_USER}
spring.datasource.password=${DB_PASSWD}
spring.datasource.driver-class-name=com.mysql.cj.jdbc.Driver
#spring.jpa.show-sql: true

• spring.jpa.hibernate.ddl-auto=update — database option;
• spring.datasource.url=jdbc:mysql://${DB_HOST}:3306/${DB_NAME} — address of the database server;
• spring.datasource.username=${DB_USER} — database username;
• spring.datasource.password=${DB_PASSWD} — database password;
• spring.datasource.driver-class-name=com.mysql.cj.jdbc.Driver — connection driver;
• #spring.jpa.show-sql: true — uncomment this option to output the MySQL statements to the stdout. This option is useful for creating database migrations.

Note that some of the parameters are specified via environment variables, e.g., ${DB_USER} or ${DB_PASSWD}.

Great, the database and the application are ready to be deployed.

Initializing and migrating the database

There are several ways to initialize and migrate a database when deploying applications to Kubernetes. We will use one straightforward yet efficient method.

The Hibernate module built into our application performs one of the actions specified in the spring.jpa.hibernate.ddl-auto parameter of the application.properties file during the application startup. There are four main methods of the module’s operation:

• validate: validate the database against the specified entities. Validation is better performed using a third-party validator such as Flyway (you can plug it in as a Maven dependency). This method is best for situations when the application is complete, and you only need to check that the database fits the structure you want or prepare a clean database to use with the application;
• update: update the database structure dynamically during operation. This method is used during development because it automatically adapts the database to entity changes;
• create: deletes data from the database and recreates tables before each application run;
• create-drop: this method is similar to the previous one, except that it deletes everything from the database after the session ends.

Either method implies that you need to make sure that MySQL is running and available for the application before starting it. So let’s edit the application’s Dockerfile by adding commands to install mysql-client in the app container.

FROM eclipse-temurin:11-alpine AS builder
COPY . /src
WORKDIR /src
RUN ./mvnw clean package -DskipTests

FROM eclipse-temurin:11-alpine as backend
# Installing the mysql-client.
RUN apk add -U mysql-client
WORKDIR /app
COPY --from=builder /src/target/*.jar ./app.jar
EXPOSE 8080

FROM nginx:stable-alpine as frontend
WORKDIR /www
ADD src/main/resources/static /www/static/
COPY .werf/nginx.conf /etc/nginx/nginx.conf

Add a database availability check to the deployment (it will be run before the application start):

apiVersion: apps/v1
kind: Deployment
metadata:
  name: werf-guide-app
spec:
  replicas: 1
  selector:
    matchLabels:
      app: werf-guide-app
  template:
    metadata:
      labels:
        app: werf-guide-app
    spec:
      imagePullSecrets:
      - name: registrysecret
      containers:
      - name: backend
        image: {{ .Values.werf.image.backend }}
        command: 
        - sh
        - -euc
        - |
          is_mysql_available() {
            tries=$1
            i=0
            while [ $i -lt $tries ]; do
              mysqladmin -h mysql -P 3306 -u root -p=password ping || return 1
              i=$((i+1))
              sleep 1
            done
          }
          # Waiting for `mysqladmin ping` to run 10 times in a row.
          until is_mysql_available 10; do
            sleep 1
          done
          # Start the app
          java -jar ./app.jar

        ports:
        - containerPort: 8080
        env:
        - name: LOGGING_LEVEL_ORG_SPRINGFRAMEWORK_WEB
          value: INFO
        - name: DB_HOST
          value: mysql
        - name: DB_NAME
          value: werf-guide-app
        - name: DB_USER
          value: root
        - name: DB_PASSWD
          value: password
      - name: frontend
        image: {{ .Values.werf.image.frontend }}
        ports:
        - containerPort: 80

In the above listing, we also passed the database connection parameters to the environment variables.

Testing the application/database

Let’s deploy the application:

werf converge --repo <DOCKER HUB USERNAME>/werf-guide-app

You should see the following output:

┌ ⛵ image backend
│ Use cache image for backend/dockerfile
│      name: <DOCKER HUB USERNAME>/werf-guide-app:3c1d990b76b29e3e53d4913607207f8d3060e23a94442c7c3c25c01d-1642762275246
│        id: 2cb054a9d1e1
│   created: 2022-01-21 13:51:14 +0000 UTC
│      size: 232.7 MiB
└ ⛵ image backend (4.06 seconds)

┌ ⛵ image frontend
│ Use cache image for frontend/dockerfile
│      name: <DOCKER HUB USERNAME>/werf-guide-app:4d7fe10a14b3d39d37a747bf016e9e8557c5a6d7061cea9d57f2ffd0-1640809566489
│        id: 4325c3e47f17
│   created: 2022-10-29 23:26:06 +0000 UTC
│      size: 9.6 MiB
└ ⛵ image frontend (2.82 seconds)

┌ Waiting for release resources to become ready
│ ┌ Status progress
│ │ DEPLOYMENT                                                                                                                                                REPLICAS                     AVAILABLE                      UP-TO-DATE                                          
│ │ werf-guide-app                                                                                                                                            2/1                          1                              1                                              ↵
│ │      
│ │ │   POD                                                         READY                 RESTARTS                      STATUS                                ---                                                                                                             
│ │ ├── guide-app-6c7cbc8b8b-pw7qf                                  0/2                   0                             ContainerCreating                     Waiting for: replicas 2->1                                                                                      
│ │ └── guide-app-7d5d5f74c6-lflsv                                  2/2                   2                             Running                               
│ │ STATEFULSET                                                                                                                                               REPLICAS                     READY                          UP-TO-DATE                                          
│ │ mysql                                                                                                                                                     1/1                          1                              1                                              ↵
│ │      
│ │ │   POD                                                         READY                 RESTARTS                      STATUS                                                                                                                                                
│ │ └── 0                                                           1/1                   0                             Running                               
│ └ Status progress
│ 
│ ┌ Status progress
│ │ DEPLOYMENT                                                                                                                                                REPLICAS                     AVAILABLE                      UP-TO-DATE                                          
│ │ werf-guide-app                                                                                                                                            2->1/1                       1                              1                                                   
│ │ │   POD                                                         READY                 RESTARTS                      STATUS                                                                                                                                                
│ │ ├── guide-app-6c7cbc8b8b-pw7qf                                  2/2                   0                             ContainerCreating -> Running          
│ │ └── guide-app-7d5d5f74c6-lflsv                                  2/2                   2                             Running -> Terminating                
│ │ STATEFULSET                                                                                                                                               REPLICAS                     READY                          UP-TO-DATE                                          
│ │ mysql                                                                                                                                                     1/1                          1                              1                                              ↵
│ │      
│ │ │   POD                                                         READY                 RESTARTS                      STATUS                                                                                                                                                
│ │ └── 0                                                           1/1                   0                             Running                               
│ └ Status progress
└ Waiting for release resources to become ready (33.78 seconds)

Release "werf-guide-app" has been upgraded. Happy Helming!
NAME: werf-guide-app
LAST DEPLOYED: Fri Jan 21 13:55:56 2022
NAMESPACE: werf-guide-app
STATUS: deployed
REVISION: 51
TEST SUITE: None
Running time 41.07 seconds

Don’t worry if the process seems to be stuck at this point and many errors appear in the messages. This happens due to checking the MySQL status; you just need to wait a bit when it’s done (usually, it takes no more than 1-2 minutes).

Now let’s try to access the /say endpoint that retrieves the data from the database:

curl http://werf-guide-app.test/say

Since the database is still empty, it should return the following message:

I have nothing to say.

Let’s save some data to the database using /remember:

curl "http://werf-guide-app.test/remember?answer=Love+you&name=sweetie"

The database must respond with the following:

Got it.

Let’s try to retrieve the data from the database using the /say endpoint once again:

curl http://werf-guide-app.test/say

If successful, you will see the following output:

Love you, sweetie!

You can also make sure that the data is in the database by directly querying the table contents:

kubectl exec -it statefulset/mysql -- mysql -ppassword -e "SELECT * from talkers" werf-guide-app

You should see the following output:

+----+----------+---------+
| id | answer   | name    |
+----+----------+---------+
|  1 | Love you | sweetie |
+----+----------+---------+

Done!

In this chapter, we turned our application into a stateful one by connecting it to the corresponding database. We deployed the database to the Kubernetes cluster, initialized it, and performed necessary DB migrations. Note that the above approach should work well with any relational database.

As usual, you can see all the changes made in this chapter by running the commands provided at the beginning.