Fariz Fadian: Framework

Wednesday, April 1, 2020

Framework

Spring Cloud Gateway Example

Fariz Fadian April 01, 2020 Leave a Reply

In a previous tutorial we had implemented API Gateway using Netflix Zuul Component. However Zuul is a blocking API. A blocking gateway api makes use of as many threads as the number of incoming requests. So this approach is more resource intensive. If no threads are available to process incoming request then the request has to wait in queue.
In this tutorial we will be implementing API Gateway using Spring Cloud Gateway. Spring Cloud Gateway is a non blocking API. When using non blocking API, a thread is always available to process the incoming request. These request are then processed asynchronously in the background and once completed the response is returned. So no incoming request never gets blocked when using Spring Cloud Gateway.
We will first look at what is API gateway and why are they needed. Then we will be exploring the Spring Cloud Gateway Architecture and implement an API Gateway using it.

Video

This tutorial is explained in the below Youtube Video.

What is an API Gateway? Why do we need it?

An API Gateway acts as a single entry point for a collection of microservices. Any external client cannot access the microservices directly but can access them only through the application gateway
In a real world scenario an external client can be any one of the three-

Mobile Application
Desktop Application
External Services or third party Apps

The advantages of this approach are as follows-

This improves the security of the microservices as we limit the access of external calls to all our services.
The cross cutting concerns like authentication, monitoring/metrics, and resiliency will be needed to be implemented only in the API Gateway as all our calls will be routed through it.
The client does not know about the internal architecture of our microservices system. Client will not be able to determine the location of the microservice instances.
Simplifies client interaction as he will need to access only a single service for all the requirements.

Spring Cloud Gateway Architecture

Spring Cloud Gateway is API Gateway implementation by Spring Cloud team on top of Spring reactive ecosystem. It consists of the following building blocks-

Route: Route the basic building block of the gateway. It consists of
- ID
- destination URI
- Collection of predicates and a collection of filters
A route is matched if aggregate predicate is true.
Predicate: This is similar to Java 8 Function Predicate. Using this functionality we can match HTTP request, such as headers , url, cookies or parameters.
Filter: These are instances Spring Framework GatewayFilter. Using this we can modify the request or response as per the requirement. We will be looking at filters in detail in the next tutorial - Spring Cloud Tutorial - Spring Cloud Gateway Filters Example

When the client makes a request to the Spring Cloud Gateway, the Gateway Handler Mapping first checks if the request matches a route. This matching is done using the predicates. If it matches the predicate then the request is sent to the filters.

Implementing Spring Cloud Gateway

Using Spring Cloud Gateway we can create routes in either of the two ways -

Use java based configuration to programmatically create routes
Use property based configuration(i.e application.properties or application.yml) to create routes.

In this tutorial we will be implementing Spring Cloud Gateway using both configurations.
We will be implementing Spring Cloud Gateway application which routes request to two other microservices depending on the url pattern.

Implement First Microservice

The Maven project will be as follows-
spring cloud first microservice

The pom.xml will be as follows:

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
 xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
 <modelVersion>4.0.0</modelVersion>
 <parent>
  <groupId>org.springframework.boot</groupId>
  <artifactId>spring-boot-starter-parent</artifactId>
  <version>2.1.7.RELEASE</version>
  <relativePath /> <!-- lookup parent from repository -->
 </parent>
 <groupId>com.javainuse</groupId>
 <artifactId>first-service</artifactId>
 <version>0.0.1-SNAPSHOT</version>

 <properties>
  <java.version>1.8</java.version>
 </properties>

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

</project>

Define the application.yml as follows-

spring:
  application:
    name: first-service
server:
  port: 8081

Create a Controller class that exposes the GET REST service as follows-

package com.javainuse.controller;

import org.springframework.web.bind.annotation.*;

@RestController
@RequestMapping("/employee")
public class FirstController {

 @GetMapping("/message")
 public String test() {
  return "Hello JavaInUse Called in First Service";
 }
}

Create the bootstrap class with the @SpringBootApplication annotation

package com.javainuse;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication
public class FirstApplication {

 public static void main(String[] args) {
  SpringApplication.run(FirstApplication.class, args);
 }

}

Implement Second Microservice

The Maven project will be as follows-
spring cloud second microservice

The pom.xml will be as follows-

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
 xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
 <modelVersion>4.0.0</modelVersion>
 <parent>
  <groupId>org.springframework.boot</groupId>
  <artifactId>spring-boot-starter-parent</artifactId>
  <version>2.1.7.RELEASE</version>
  <relativePath /> <!-- lookup parent from repository -->
 </parent>
 <groupId>com.javainuse</groupId>
 <artifactId>second-service</artifactId>
 <version>0.0.1-SNAPSHOT</version>

 <properties>
  <java.version>1.8</java.version>
 </properties>

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

</project>

Define the application.properties as follows-

spring:
  application:
    name: second-service
server:
  port: 8082

Create a Controller class that exposes the GET REST service as follows-

package com.javainuse.controller;

import org.springframework.web.bind.annotation.*;

@RestController
@RequestMapping("/consumer")
public class SecondController {

 @GetMapping("/message")
 public String test() {
  return "Hello JavaInUse Called in Second Service";
 }

}

Create the bootstrap class with the @SpringBootApplication annotation

package com.javainuse;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication
public class SecondApplication {

 public static void main(String[] args) {
  SpringApplication.run(SecondApplication.class, args);
 }
}

Implement Spring Cloud Gateway using property based config

The Maven project will be as follows-
spring cloud gateway microservice

The pom.xml will be as follows-

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
 xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
 <modelVersion>4.0.0</modelVersion>
 <groupId>com.javainuse</groupId>
 <artifactId>cloud-gateway-service</artifactId>
 <version>0.0.1-SNAPSHOT</version>
 <name>gateway-service</name>

 <properties>
  <java.version>1.8</java.version>
  <spring-cloud.version>Greenwich.SR2</spring-cloud.version>
 </properties>

 <dependencies>
  <dependency>
   <groupId>org.springframework.cloud</groupId>
   <artifactId>spring-cloud-starter-gateway</artifactId>
  </dependency>
 </dependencies>

 <dependencyManagement>
  <dependencies>
   <dependency>
    <groupId>org.springframework.cloud</groupId>
    <artifactId>spring-cloud-dependencies</artifactId>
    <version>${spring-cloud.version}</version>
    <type>pom</type>
    <scope>import</scope>
   </dependency>
  </dependencies>
 </dependencyManagement>
 <repositories>
  <repository>
   <id>spring-milestones</id>
   <name>Spring Milestones</name>
   <url>https://repo.spring.io/milestone</url>
  </repository>
 </repositories>
 <build>
  <plugins>
   <plugin>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-maven-plugin</artifactId>
   </plugin>
  </plugins>
 </build>

</project>

Define the application.yml as follows-

server:
  port: 8080

spring:
  cloud:
    gateway:
      routes:
      - id: employeeModule
        uri: http://localhost:8081/
        predicates:
        - Path=/employee/**
      - id: consumerModule
        uri: http://localhost:8082/
        predicates:
        - Path=/consumer/**

Create the bootstrap class with the @SpringBootApplication annotation

package com.javainuse;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication
public class APIGatewayApplication {

 public static void main(String[] args) {
  SpringApplication.run(APIGatewayApplication.class, args);
 }

}

Start the three microservices we have developed-

Go to url - localhost:8080/employee/message
Go to url - localhost:8080/consumer/message

Implement Spring Cloud Gateway using Java based config

The Maven project will be as follows-
spring cloud gateway config microservice

The pom.xml will be as follows-

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
 xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
 <modelVersion>4.0.0</modelVersion>
 <groupId>com.javainuse</groupId>
 <artifactId>cloud-gateway-service</artifactId>
 <version>0.0.1-SNAPSHOT</version>
 <name>gateway-service</name>

 <properties>
  <java.version>1.8</java.version>
  <spring-cloud.version>Greenwich.SR2</spring-cloud.version>
 </properties>

 <dependencies>
  <dependency>
   <groupId>org.springframework.cloud</groupId>
   <artifactId>spring-cloud-starter-gateway</artifactId>
  </dependency>
 </dependencies>

 <dependencyManagement>
  <dependencies>
   <dependency>
    <groupId>org.springframework.cloud</groupId>
    <artifactId>spring-cloud-dependencies</artifactId>
    <version>${spring-cloud.version}</version>
    <type>pom</type>
    <scope>import</scope>
   </dependency>
  </dependencies>
 </dependencyManagement>
 <repositories>
  <repository>
   <id>spring-milestones</id>
   <name>Spring Milestones</name>
   <url>https://repo.spring.io/milestone</url>
  </repository>
 </repositories>
 <build>
  <plugins>
   <plugin>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-maven-plugin</artifactId>
   </plugin>
  </plugins>
 </build>

</project>

Define the application.yml as follows-

server:
  port: 8080

Create the configuration class where we define the route configurations. Gateway Handler resolves route configurations by using RouteLocator Bean.

package com.javainuse.config;

import org.springframework.cloud.gateway.route.RouteLocator;
import org.springframework.cloud.gateway.route.builder.RouteLocatorBuilder;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

@Configuration
public class SpringCloudConfig {

    @Bean
    public RouteLocator gatewayRoutes(RouteLocatorBuilder builder) {
        return builder.routes()
                .route(r -> r.path("/employee/**")
                        .uri("http://localhost:8081/")
                        .id("employeeModule"))

                .route(r -> r.path("/consumer/**")
                        .uri("http://localhost:8082/")
                        .id("consumerModule"))
                .build();
    }

}

Create the bootstrap class with the @SpringBootApplication annotation

package com.javainuse;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication
public class APIGatewayApplication {

 public static void main(String[] args) {
  SpringApplication.run(APIGatewayApplication.class, args);
 }

}

Start the three microservices we have developed-

Go to url - localhost:8080/employee/message
Go to url - localhost:8080/consumer/message

Reference:

Javainuse.com - Spring Cloud Gateway

Tuesday, March 31, 2020

Framework

API Cache Cluster Container Docker Flask Framework Programming Python Redis REST Virtual Machine VM

Docker Compose + Python + Flask Example

Fariz Fadian March 31, 2020

On this page you build a simple Python web application running on Docker Compose. The application uses the Flask framework and maintains a hit counter in Redis. While the sample uses Python, the concepts demonstrated here should be understandable even if you’re not familiar with it.

Prerequisites

Make sure you have already installed both Docker Engine and Docker Compose. You don’t need to install Python or Redis, as both are provided by Docker images.

Step 1: Setup

Define the application dependencies.

Create a directory for the project:
```
$ mkdir composetest
$ cd composetest
```
Create a file called app.py in your project directory and paste this in:
```
import time

import redis
from flask import Flask

app = Flask(__name__)
cache = redis.Redis(host='redis', port=6379)


def get_hit_count():
    retries = 5
    while True:
        try:
            return cache.incr('hits')
        except redis.exceptions.ConnectionError as exc:
            if retries == 0:
                raise exc
            retries -= 1
            time.sleep(0.5)


@app.route('/')
def hello():
    count = get_hit_count()
    return 'Hello World! I have been seen {} times.\n'.format(count)
```
In this example, redis is the hostname of the redis container on the application’s network. We use the default port for Redis, 6379.

Handling transient errors

Note the way the get_hit_count function is written. This basic retry loop lets us attempt our request multiple times if the redis service is not available. This is useful at startup while the application comes online, but also makes our application more resilient if the Redis service needs to be restarted anytime during the app’s lifetime. In a cluster, this also helps handling momentary connection drops between nodes.
Create another file called requirements.txt in your project directory and paste this in:
```
flask
redis
```

Step 2: Create a Dockerfile

In this step, you write a Dockerfile that builds a Docker image. The image contains all the dependencies the Python application requires, including Python itself.

In your project directory, create a file named Dockerfile and paste the following:

FROM python:3.7-alpine
WORKDIR /code
ENV FLASK_APP app.py
ENV FLASK_RUN_HOST 0.0.0.0
RUN apk add --no-cache gcc musl-dev linux-headers
COPY requirements.txt requirements.txt
RUN pip install -r requirements.txt
COPY . .
CMD ["flask", "run"]

This tells Docker to:

Build an image starting with the Python 3.7 image.
Set the working directory to /code.
Set environment variables used by the flask command.
Install gcc so Python packages such as MarkupSafe and SQLAlchemy can compile speedups.
Copy requirements.txt and install the Python dependencies.
Copy the current directory . in the project to the workdir . in the image.
Set the default command for the container to flask run.

For more information on how to write Dockerfiles, see the Docker user guide and the Dockerfile reference.

Step 3: Define services in a Compose file

Create a file called docker-compose.yml in your project directory and paste the following:

version: '3'
services:
  web:
    build: .
    ports:
      - "5000:5000"
  redis:
    image: "redis:alpine"

This Compose file defines two services: web and redis.

Web service

The web service uses an image that’s built from the Dockerfile in the current directory. It then binds the container and the host machine to the exposed port, 5000. This example service uses the default port for the Flask web server, 5000.

Redis service

The redis service uses a public Redis image pulled from the Docker Hub registry.

Step 4: Build and run your app with Compose

From your project directory, start up your application by running docker-compose up.

$ docker-compose up
Creating network "composetest_default" with the default driver
Creating composetest_web_1 ...
Creating composetest_redis_1 ...
Creating composetest_web_1
Creating composetest_redis_1 ... done
Attaching to composetest_web_1, composetest_redis_1
web_1    |  * Running on http://0.0.0.0:5000/ (Press CTRL+C to quit)
redis_1  | 1:C 17 Aug 22:11:10.480 # oO0OoO0OoO0Oo Redis is starting oO0OoO0OoO0Oo
redis_1  | 1:C 17 Aug 22:11:10.480 # Redis version=4.0.1, bits=64, commit=00000000, modified=0, pid=1, just started
redis_1  | 1:C 17 Aug 22:11:10.480 # Warning: no config file specified, using the default config. In order to specify a config file use redis-server /path/to/redis.conf
web_1    |  * Restarting with stat
redis_1  | 1:M 17 Aug 22:11:10.483 * Running mode=standalone, port=6379.
redis_1  | 1:M 17 Aug 22:11:10.483 # WARNING: The TCP backlog setting of 511 cannot be enforced because /proc/sys/net/core/somaxconn is set to the lower value of 128.
web_1    |  * Debugger is active!
redis_1  | 1:M 17 Aug 22:11:10.483 # Server initialized
redis_1  | 1:M 17 Aug 22:11:10.483 # WARNING you have Transparent Huge Pages (THP) support enabled in your kernel. This will create latency and memory usage issues with Redis. To fix this issue run the command 'echo never > /sys/kernel/mm/transparent_hugepage/enabled' as root, and add it to your /etc/rc.local in order to retain the setting after a reboot. Redis must be restarted after THP is disabled.
web_1    |  * Debugger PIN: 330-787-903
redis_1  | 1:M 17 Aug 22:11:10.483 * Ready to accept connections

Compose pulls a Redis image, builds an image for your code, and starts the services you defined. In this case, the code is statically copied into the image at build time.

Enter http://localhost:5000/ in a browser to see the application running.

If you’re using Docker natively on Linux, Docker Desktop for Mac, or Docker Desktop for Windows, then the web app should now be listening on port 5000 on your Docker daemon host. Point your web browser to http://localhost:5000 to find the Hello World message. If this doesn’t resolve, you can also try http://127.0.0.1:5000.

If you’re using Docker Machine on a Mac or Windows, use docker-machine ip MACHINE_VM to get the IP address of your Docker host. Then, open http://MACHINE_VM_IP:5000 in a browser.

You should see a message in your browser saying:
```
Hello World! I have been seen 1 times.
```
Refresh the page.

The number should increment.
```
Hello World! I have been seen 2 times.
```

Switch to another terminal window, and type docker image ls to list local images.

Listing images at this point should return redis and web.

$ docker image ls
REPOSITORY              TAG                 IMAGE ID            CREATED             SIZE
composetest_web         latest              e2c21aa48cc1        4 minutes ago       93.8MB
python                  3.4-alpine          84e6077c7ab6        7 days ago          82.5MB
redis                   alpine              9d8fa9aa0e5b        3 weeks ago         27.5MB

You can inspect images with docker inspect <tag or id>.

Stop the application, either by running docker-compose down from within your project directory in the second terminal, or by hitting CTRL+C in the original terminal where you started the app.

Step 5: Edit the Compose file to add a bind mount

Edit docker-compose.yml in your project directory to add a bind mount for the web service:

version: '3'
services:
  web:
    build: .
    ports:
      - "5000:5000"
    volumes:
      - .:/code
    environment:
      FLASK_ENV: development
  redis:
    image: "redis:alpine"

The new volumes key mounts the project directory (current directory) on the host to /code inside the container, allowing you to modify the code on the fly, without having to rebuild the image. The environment key sets the FLASK_ENV environment variable, which tells flask run to run in development mode and reload the code on change. This mode should only be used in development.

Step 6: Re-build and run the app with Compose

From your project directory, type docker-compose up to build the app with the updated Compose file, and run it.

$ docker-compose up
Creating network "composetest_default" with the default driver
Creating composetest_web_1 ...
Creating composetest_redis_1 ...
Creating composetest_web_1
Creating composetest_redis_1 ... done
Attaching to composetest_web_1, composetest_redis_1
web_1    |  * Running on http://0.0.0.0:5000/ (Press CTRL+C to quit)
...

Check the Hello World message in a web browser again, and refresh to see the count increment.

Shared folders, volumes, and bind mounts

If your project is outside of the Users directory (cd ~), then you need to share the drive or location of the Dockerfile and volume you are using. If you get runtime errors indicating an application file is not found, a volume mount is denied, or a service cannot start, try enabling file or drive sharing. Volume mounting requires shared drives for projects that live outside of C:\Users (Windows) or /Users (Mac), and is required for any project on Docker Desktop for Windows that uses Linux containers. For more information, see Shared Drives on Docker Desktop for Windows, File sharing on Docker for Mac, and the general examples on how to Manage data in containers.

If you are using Oracle VirtualBox on an older Windows OS, you might encounter an issue with shared folders as described in this VB trouble ticket. Newer Windows systems meet the requirements for Docker Desktop for Windows and do not need VirtualBox.

Step 7: Update the application

Because the application code is now mounted into the container using a volume, you can make changes to its code and see the changes instantly, without having to rebuild the image.

Change the greeting in app.py and save it. For example, change the Hello World! message to Hello from Docker!:
```
return 'Hello from Docker! I have been seen {} times.\n'.format(count)
```
Refresh the app in your browser. The greeting should be updated, and the counter should still be incrementing.

Step 8: Experiment with some other commands

If you want to run your services in the background, you can pass the -d flag (for “detached” mode) to docker-compose up and use docker-compose ps to see what is currently running:

$ docker-compose up -d
Starting composetest_redis_1...
Starting composetest_web_1...

$ docker-compose ps
Name                 Command            State       Ports
-------------------------------------------------------------------
composetest_redis_1   /usr/local/bin/run         Up
composetest_web_1     /bin/sh -c python app.py   Up      5000->5000/tcp

The docker-compose run command allows you to run one-off commands for your services. For example, to see what environment variables are available to the web service:

$ docker-compose run web env

See docker-compose --help to see other available commands. You can also install command completion for the bash and zsh shell, which also shows you available commands.

If you started Compose with docker-compose up -d, stop your services once you’ve finished with them:

$ docker-compose stop

You can bring everything down, removing the containers entirely, with the down command. Pass --volumes to also remove the data volume used by the Redis container:

$ docker-compose down --volumes

At this point, you have seen the basics of how Compose works.

Where to go next

Next, try the quick start guide for Django, Rails, or WordPress
Explore the full list of Compose commands
Compose configuration file reference
To learn more about volumes and bind mounts, see Manage data in Docker

documentation, docs, docker, compose, orchestration, containers

Reference:

Docker.com - Getting Started Docker Compose

Wednesday, April 1, 2020

Spring Cloud Gateway Example

What is an API Gateway? Why do we need it?

Spring Cloud Gateway Architecture

Implementing Spring Cloud Gateway

Implement First Microservice

Implement Second Microservice

Implement Spring Cloud Gateway using property based config

Implement Spring Cloud Gateway using Java based config

Tuesday, March 31, 2020

Docker Compose + Python + Flask Example

Prerequisites

Step 1: Setup

Step 2: Create a Dockerfile

Step 3: Define services in a Compose file

Web service

Redis service

Step 4: Build and run your app with Compose

Step 5: Edit the Compose file to add a bind mount

Step 6: Re-build and run the app with Compose

Step 7: Update the application

Step 8: Experiment with some other commands

Where to go next

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