Serving assets

In this chapter, you will learn how to work with static files and serve them to the client correctly.

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/030_assets/* .
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/030_assets/. .
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/020_logging ~/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/030_assets/* .
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/020_logging ~/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/030_assets/. .
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

Adding an /image page to the application

Let’s add a new /image endpoint to our application. It will return a page with a set of static files. We will use JS-, CSS-, and media files will be served by standard Spring Boot means to bundle all JS, CSS, and media files.

Currently, our application provides a basic API with no means to manage static files and frontend code.

To turn this API into a simple web application, you need to modify it as follows: First, add the Thymeleaf template engine to the project by inserting the corresponding dependency into pom.xml.

...
<dependency>
	<groupId>org.springframework.boot</groupId>
	<artifactId>spring-boot-starter-thymeleaf</artifactId>
</dependency>

Create a directory structure to store static files:

$ tree ./src/main/resources/
./src/main/resources/
├── application.properties
├── log4j2-spring.xml
├── static
│   ├── images
│   │   └── werf-logo.svg
│   ├── javascripts
│   │   └── image.js
│   └── stylesheets
│       └── site.css
└── templates
    ├── image.html
    └── index.html

Copy static files to the corresponding subdirectories in the static directory. Copy Thymeleaf page templates to the templates directory.

Configure the application to serve files from the static directory. To do this, create a MvcConfig configuration class:

package io.werf.werfguidesapp.config;

import org.springframework.context.annotation.Configuration;
import org.springframework.web.servlet.config.annotation.ResourceHandlerRegistry;
import org.springframework.web.servlet.config.annotation.WebMvcConfigurer;

@Configuration
public class MvcConfig implements WebMvcConfigurer {

	@Override
	public void addResourceHandlers(ResourceHandlerRegistry registry) {
		registry.addResourceHandler("/static/**").addResourceLocations("classpath:/static/");
	}

}

In it, specify that the static directory contents are freely accessible from outside at the /static endpoint.

Add new controllers to handle requests to the / and /image endpoints:

package io.werf.werfguidesapp.controllers;

import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.GetMapping;


@Controller
public class ImageController {

	@GetMapping("/")
	public String MainPath() {
		return "index";
	}
	
	@GetMapping("/image")
	public String Image() {
		return "image";
	}
}

The controllers access the Thymeleaf template files (you have already set their location above). Create them:

<html>
  <head>
    <title>Werf Guide App</title>
    <link rel="stylesheet" href="static/stylesheets/site.css" />
  </head>

  <body>
    <h1>Wef Guide App based on Express</h1>
    <p>Welcome to Werf guide. Visit <a href="/image">the image page</a>.</p>
  </body>
</html>

<!DOCTYPE html>
<html>
  <head>
    <title>Werf Logo</title>
    <meta name="viewport" content="width=device-width,initial-scale=1" />
    <link rel="stylesheet" href="static/stylesheets/site.css" />
    <script src="static/javascripts/image.js"></script>
  </head>

  <body>
    <div id="container">
      <!-- The "Get image" button; it will generate an Ajax request when clicked. -->
      <button type="button" id="show-image-btn">Get image</button>
    </div>
  </body>
</html>

Clicking the Get image button must result in an Ajax request that pulls and displays the SVG image:

window.onload=function(){
  var btn = document.getElementById("show-image-btn")
  btn.addEventListener("click", _ => {
      fetch("/static/images/werf-logo.svg")
        .then((data) => data.text())
        .then((html) => {
          const svgContainer = document.getElementById("container")
          svgContainer.insertAdjacentHTML("beforeend", html)
          var svg = svgContainer.getElementsByTagName("svg")[0]
          svg.setAttribute("id", "image")
          btn.remove()
        }
      )
    }
  )
}

Note that our page also uses the static/stylesheets/site.css file.

The application now has a new endpoint called /image in addition to the /ping endpoint we made in previous chapters. This new endpoint displays a page that uses different types of static files.

The commands provided at the beginning of the chapter allow you to view a complete, exhaustive list of the changes made to the application in the current chapter.

Serving static files

Currently, Spring Boot serves static files using built-in tools. Using a reverse proxy like NGINX is a more efficient and robust approach. This is because the reverse proxy distributes static files much more efficiently than Spring Boot.

There are several ways to deploy the Spring Boot application behind the reverse proxy in Kubernetes. We will use a popular and straightforward method that nevertheless scales well. As part of it, the NGINX container is deployed to each Pod with the Spring Boot container. This auxiliary container serves as a proxy for all requests except for static file requests. The NGINX container is responsible for the distribution of static files.

Now, let’s get to the implementation.

Making changes to the build and deploy process

First of all, we have to make changes to the application build process. Now we need to build an NGINX image in addition to the Spring Boot one. This NGINX image must have all the static files to serve to the client:

# Here, a multi-stage build is used to assemble the image.
# The image for the project assembly.
FROM eclipse-temurin:11-alpine AS builder
# Copy the source code of the application.
COPY . /src
WORKDIR /src
# Run Maven to build the project.
RUN ./mvnw clean package

# The image to deploy to the cluster.
FROM eclipse-temurin:11-alpine as backend
WORKDIR /app
# Copy the project executable from the build image.
COPY --from=builder /src/target/*.jar ./app.jar
EXPOSE 8080
ENTRYPOINT ["java","-jar","./app.jar"]

# The NGINX image that contains the static files.
FROM nginx:stable-alpine as frontend
WORKDIR /www
# Copy static files.
COPY src/main/resources/static /www/static/
# Copy NGINX configuration.
COPY .werf/nginx.conf /etc/nginx/nginx.conf

The NGINX config will be added to the NGINX image during the build:

user nginx;
worker_processes 1;
pid /run/nginx.pid;

events {
  worker_connections 1024;
}

http {
  include /etc/nginx/mime.types;
  default_type application/octet-stream;

  upstream backend {
    server 127.0.0.1:8080 fail_timeout=0;
  }

  server {
    listen 80;
    server_name _;

    root /www;

    client_max_body_size 100M;
    keepalive_timeout 10s;

    # For the /static path, serve the assets directly from the NGINX container file system.
    location /static {

      expires 1y;
      add_header Cache-Control public;
      add_header Last-Modified "";
      add_header ETag "";

      # If possible, serve pre-compressed files (instead of compressing them on the fly).
      gzip_static on;

      access_log off;

      try_files $uri =404;
    }

    # Serve media assets (images, etc.) directly from the NGINX container file system, 
    # but turn off gzip compression.
    location /static/images {
      expires 1y;
      add_header Cache-Control public;
      add_header Last-Modified "";
      add_header ETag "";

      access_log off;

      try_files $uri =404;
    }

    # All requests, except for asset requests, are sent to the Spring Boot backend.
    location / {
      proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
      proxy_set_header X-Real-IP $remote_addr;
      proxy_set_header X-Forwarded-Proto $scheme;
      proxy_set_header Host $http_host;
      proxy_redirect off;

      proxy_pass http://backend;
    }
  }
}

Let’s update werf.yaml so that werf will build two images (backend, frontend) instead of one:

project: werf-guide-app
configVersion: 1

---
image: backend
dockerfile: Dockerfile
target: backend

---
image: frontend
dockerfile: Dockerfile
target: frontend

Add a new NGINX container to the application Deployment:

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 }}
        ports:
        - containerPort: 8080
        env:
        - name: LOGGING_LEVEL_ORG_SPRINGFRAMEWORK_WEB
          value: INFO
      - name: frontend
        image: {{ .Values.werf.image.frontend }}
        ports:
        - containerPort: 80

Service and Ingress should now connect to port 80 instead of 8080 so that all requests are routed through the NGINX proxy instead of sending them directly to our application:

apiVersion: v1
kind: Service
metadata:
  name: werf-guide-app
spec:
  selector:
    app: werf-guide-app
  ports:
  - name: http
    port: 80

apiVersion: networking.k8s.io/v1
kind: Ingress
metadata:
  annotations:
    kubernetes.io/ingress.class: nginx
  name: werf-guide-app
spec:
  rules:
  - host: werf-guide-app.test
    http:
      paths:
      - path: /
        pathType: Prefix
        backend:
          service:
            name: werf-guide-app
            port:
              number: 80

Checking that everything works as expected

Now we have to re-deploy our application:

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

You should see the following output:

...
┌ Concurrent builds plan (no more than 5 images at the same time)
│ Set #0:
│ - ⛵ image backend
│ - ⛵ image frontend
└ Concurrent builds plan (no more than 5 images at the same time)

┌ ⛵ image backend
│ Use cache image for backend/dockerfile
│      name: <DOCKER HUB USERNAME>/werf-guide-app:0b759f60b7405e96d44b7139ada9b57a6cf92bab10de79d753b7e6bc-1642676484362
│        id: d9f9545fbd21
│   created: 2022-01-20 14:01:21 +0000 UTC
│      size: 204.0 MiB
└ ⛵ image backend (4.79 seconds)

┌ ⛵ image frontend
│ Use cache image for frontend/dockerfile
│      name: <DOCKER HUB USERNAME>/werf-guide-app:2e2e91751acd1cf77cfdbf57f9af1f21782b6cbc725f8e7c9cd31b3f-1642676498242
│        id: 5e3f3f616bae
│   created: 2022-01-20 14:01:37 +0000 UTC
│      size: 9.6 MiB
└ ⛵ image frontend (4.81 seconds)

┌ Waiting for release resources to become ready
│ ┌ Status progress
│ │ DEPLOYMENT                                                                                                                                                REPLICAS                     AVAILABLE                      UP-TO-DATE                                          
│ │ werf-guide-app                                                                                                                                            1/1                          1                              1                                              ↵
│ │      
│ └ Status progress
└ Waiting for release resources to become ready (0.03 seconds)

Release "werf-guide-app" has been upgraded. Happy Helming!
NAME: werf-guide-app
LAST DEPLOYED: Thu Jan 20 14:06:30 2022
NAMESPACE: werf-guide-app
STATUS: deployed
REVISION: 50
TEST SUITE: None
Running time 9.47 seconds

We omitted the full build output here because Maven generates a lot of messages while downloading all of the dependencies.

Go to http://werf-guide-app.test/image in your browser and click on the Get image button. You should see the following output:

Note which resources were requested and which links were used (the last resource here was retrieved via the Ajax request):

Now our application not only provides an API but boasts a set of tools to manage static and JavaScript files effectively.

Furthermore, our application can handle a high load since many requests for static files will not affect the operation of the application as a whole. Note that you can quickly scale of a Spring Boot application (serves dynamic content) and NGINX (serves static content) by increasing the number of replicas in the application’s Deployment.