Connecting to a Redis instance from an App Engine flexible environment application

App Engine applications must be on the same authorized network as the Redis instance in order to access it.

Setup

If you have already installed the Google Cloud CLI and have created a Redis instance, you can skip these steps.

Install the gcloud CLI and initialize:
```
gcloud init
```
Follow the Quickstart Guide to create a Redis instance. Take note of the zone, IP address, and port of the Redis instance.

Sample application

This sample HTTP server application establishes a connection to a Redis instance from an App Engine flexible environment instance.

Clone the repository for your desired programming language and navigate to the folder that contains the sample code:

Go

git clone https://github.com/GoogleCloudPlatform/golang-samples
cd golang-samples/memorystore/redis

Java

git clone https://github.com/GoogleCloudPlatform/java-docs-samples
cd java-docs-samples/memorystore/redis

Node.js

git clone https://github.com/GoogleCloudPlatform/nodejs-docs-samples
cd nodejs-docs-samples/memorystore/redis

Python

git clone https://github.com/GoogleCloudPlatform/python-docs-samples
cd python-docs-samples/memorystore/redis

This sample application increments a Redis counter every time the / endpoint is accessed.

Go

This application uses the github.com/gomodule/redigo/redis client. Install it by running the following command:

go get github.com/gomodule/redigo/redis


// Command redis is a basic app that connects to a managed Redis instance.
package main

import (
	"fmt"
	"log"
	"net/http"
	"os"

	"github.com/gomodule/redigo/redis"
)

var redisPool *redis.Pool

func incrementHandler(w http.ResponseWriter, r *http.Request) {
	conn := redisPool.Get()
	defer conn.Close()

	counter, err := redis.Int(conn.Do("INCR", "visits"))
	if err != nil {
		http.Error(w, "Error incrementing visitor counter", http.StatusInternalServerError)
		return
	}
	fmt.Fprintf(w, "Visitor number: %d", counter)
}

func main() {
	redisHost := os.Getenv("REDISHOST")
	redisPort := os.Getenv("REDISPORT")
	redisAddr := fmt.Sprintf("%s:%s", redisHost, redisPort)

	const maxConnections = 10
	redisPool = &redis.Pool{
		MaxIdle: maxConnections,
		Dial:    func() (redis.Conn, error) { return redis.Dial("tcp", redisAddr) },
	}

	http.HandleFunc("/", incrementHandler)

	port := os.Getenv("PORT")
	if port == "" {
		port = "8080"
	}
	log.Printf("Listening on port %s", port)
	if err := http.ListenAndServe(":"+port, nil); err != nil {
		log.Fatal(err)
	}
}

Java

This application is Jetty 3.1 servlet-based.

It uses the Jedis library:

<dependency>
  <groupId>redis.clients</groupId>
  <artifactId>jedis</artifactId>
  <version>5.1.0</version>
</dependency>

The AppServletContextListener class is used to create a long-lived Redis connection pool:


package com.example.redis;

import java.io.IOException;
import java.util.Properties;
import javax.servlet.ServletContextEvent;
import javax.servlet.ServletContextListener;
import javax.servlet.annotation.WebListener;
import redis.clients.jedis.JedisPool;
import redis.clients.jedis.JedisPoolConfig;

@WebListener
public class AppServletContextListener implements ServletContextListener {

  private Properties config = new Properties();

  private JedisPool createJedisPool() throws IOException {
    String host;
    Integer port;
    config.load(
        Thread.currentThread()
            .getContextClassLoader()
            .getResourceAsStream("application.properties"));
    host = config.getProperty("redis.host");
    port = Integer.valueOf(config.getProperty("redis.port", "6379"));

    JedisPoolConfig poolConfig = new JedisPoolConfig();
    // Default : 8, consider how many concurrent connections into Redis you will need under load
    poolConfig.setMaxTotal(128);

    return new JedisPool(poolConfig, host, port);
  }

  @Override
  public void contextDestroyed(ServletContextEvent event) {
    JedisPool jedisPool = (JedisPool) event.getServletContext().getAttribute("jedisPool");
    if (jedisPool != null) {
      jedisPool.destroy();
      event.getServletContext().setAttribute("jedisPool", null);
    }
  }

  // Run this before web application is started
  @Override
  public void contextInitialized(ServletContextEvent event) {
    JedisPool jedisPool = (JedisPool) event.getServletContext().getAttribute("jedisPool");
    if (jedisPool == null) {
      try {
        jedisPool = createJedisPool();
        event.getServletContext().setAttribute("jedisPool", jedisPool);
      } catch (IOException e) {
        // handle exception
      }
    }
  }
}

The VisitCounterServlet class is a web servlet that increments a Redis counter:


package com.example.redis;

import java.io.IOException;
import java.net.SocketException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import redis.clients.jedis.Jedis;
import redis.clients.jedis.JedisPool;

@WebServlet(name = "Track visits", value = "")
public class VisitCounterServlet extends HttpServlet {

  @Override
  public void doGet(HttpServletRequest req, HttpServletResponse resp) throws IOException {
    try {
      JedisPool jedisPool = (JedisPool) req.getServletContext().getAttribute("jedisPool");

      if (jedisPool == null) {
        throw new SocketException("Error connecting to Jedis pool");
      }
      Long visits;

      try (Jedis jedis = jedisPool.getResource()) {
        visits = jedis.incr("visits");
      }

      resp.setStatus(HttpServletResponse.SC_OK);
      resp.getWriter().println("Visitor counter: " + String.valueOf(visits));
    } catch (Exception e) {
      resp.sendError(HttpServletResponse.SC_INTERNAL_SERVER_ERROR, e.getMessage());
    }
  }
}

Node.js

This application uses the redis module.

{
  "name": "memorystore-redis",
  "description": "An example of using Memorystore(Redis) with Node.js",
  "version": "0.0.1",
  "private": true,
  "license": "Apache Version 2.0",
  "author": "Google Inc.",
  "engines": {
    "node": ">=16.0.0"
  },
  "dependencies": {
    "redis": "^4.0.0"
  }
}

'use strict';
const http = require('http');
const redis = require('redis');

const REDISHOST = process.env.REDISHOST || 'localhost';
const REDISPORT = process.env.REDISPORT || 6379;

const client = redis.createClient(REDISPORT, REDISHOST);
client.on('error', err => console.error('ERR:REDIS:', err));

// create a server
http
  .createServer((req, res) => {
    // increment the visit counter
    client.incr('visits', (err, reply) => {
      if (err) {
        console.log(err);
        res.status(500).send(err.message);
        return;
      }
      res.writeHead(200, {'Content-Type': 'text/plain'});
      res.end(`Visitor number: ${reply}\n`);
    });
  })
  .listen(8080);

Python

This application uses Flask for web serving and the redis-py package to communicate with the Redis instance.

Flask==3.0.3
gunicorn==22.0.0
redis==5.2.1
Werkzeug==3.0.3

import logging
import os

from flask import Flask
import redis

app = Flask(__name__)

redis_host = os.environ.get("REDISHOST", "localhost")
redis_port = int(os.environ.get("REDISPORT", 6379))
redis_client = redis.StrictRedis(host=redis_host, port=redis_port)


@app.route("/")
def index():
    value = redis_client.incr("counter", 1)
    return f"Visitor number: {value}"


@app.errorhandler(500)
def server_error(e):
    logging.exception("An error occurred during a request.")
    return (
        """
    An internal error occurred: <pre>{}</pre>
    See logs for full stacktrace.
    """.format(
            e
        ),
        500,
    )


if __name__ == "__main__":
    # This is used when running locally. Gunicorn is used to run the
    # application on Google App Engine and Cloud Run.
    # See entrypoint in app.yaml or Dockerfile.
    app.run(host="127.0.0.1", port=8080, debug=True)

Preparing the application for deployment

To access the Redis instance, the App Engine instance must be deployed on the same authorized network as the Redis instance, and you must provide your Redis instance's connection details. You can find your Redis instance's authorized network, IP address, and port by running the following command:

 gcloud redis instances describe [INSTANCE_ID] --region [REGION]

Create an App Engine application.

Note: You can also use an existing App Engine application.

Update the app's configuration to specify the IP address, port, and network of your Redis instance:

Go

Update the gae_flex_deployment/app.yaml file:

runtime: go
env: flex

# Update with Redis instance details
env_variables:
  REDISHOST: '<REDIS_IP>'
  REDISPORT: '6379'

# Update with Redis instance network name
network:
  name: default

See Configuring your App with app.yaml for more details.

Java

Update the gae_flex_deployment/app.yaml file to specify your Redis instance's network:

runtime: java
env: flex

# Update with Redis instance network name
network:
  name: default

And update the src/main/resources/application.properties file with your Redis instance's IP address and port:

redis.host=REDIS_HOST_IP
redis.port=6379

For more information about configuring your app, see Configuring your App with app.yaml.

Node.js

Update the gae_flex_deployment/app.yaml file:

runtime: nodejs
env: flex

# Update with Redis instance details
env_variables:
  REDISHOST: '<REDIS_IP>'
  REDISPORT: '6379'

# Update with Redis instance network name
network:
  name: default

See Configuring your App with app.yaml for more details.

Python

Update the gae_flex_deployment/app.yaml file:

runtime: python
env: flex
entrypoint: gunicorn -b :$PORT main:app

runtime_config:
  python_version: 3

# Update with Redis instance IP and port
env_variables:
  REDISHOST: '<REDIS_IP>'
  REDISPORT: '6379'

# Update with Redis instance network name
network:
  name: default

See Configuring your App with app.yaml for more details.

Deploying the application to the App Engine flexible environment

To deploy the application:

Copy necessary configuration files into the source directory:
Go
Copy the app.yaml file into the source directory:
```
cp gae_flex_deployment/app.yaml .
```
Java
Copy the app.yaml file into the source directory:
```
mkdir -p src/main/appengine
cp gae_flex_deployment/app.yaml src/main/appengine/
```
Node.js
Copy the app.yaml file into the source directory:
```
cp gae_flex_deployment/app.yaml .
```
Python
Copy the app.yaml file into the source directory:
```
cp gae_flex_deployment/app.yaml .
```
Run the deploy command:
Go
```
gcloud app deploy
```
This might take a few minutes.
Java
```
mvn appengine:deploy
```
This might take a few minutes.
Node.js
```
gcloud app deploy
```
This might take a few minutes.
Python
```
gcloud app deploy
```
This might take a few minutes.

After the deployment is complete, visit your app at the following URL, replacing [PROJECT_ID] with your Google Cloud project ID:

https://[PROJECT_ID].appspot.com

The count on your Redis instance increases each time the app is visited.