Websocket API with and Redis

Websocket API with and Redis

  • This project deploys a simple Websocket API built using
  • The application runs in a container workload and uses Upstash redis to store the session data. The requests are routed using Application Load Balancer.
  • The Websocket API is work as expected even if horizontally scaled (multiple parallel instances can be added).


  • Fixed price resources:

    • Container workload (~$0.012/hour, ~$9/month)
  • There are also other resources that might incur costs (with pay-per-use pricing). If your load won't get high, these costs will be close to $0.


If you're deploying from your local machine (not from a CI/CD pipeline), you need the following prerequisites:

1. Generate your project

The command below will bootstrap the project with pre-built application code and pre-configured stacktape.yml config file.


stp init --projectId socketio-websocket-api-redis

2. Deploy your stack

  • To provision all the required infrastructure and to deploy your application to the cloud, all you need is a single command.
  • The deployment will take ~5-15 minutes. Subsequent deploys will be significantly faster.


stp deploy --stage <<stage>> --region <<region>>

stage is an arbitrary name of your environment (for example staging, production or dev-john)

region is the AWS region, where your stack will be deployed to. All the available regions are listed below.

Region name & Locationcode
Europe (Ireland)eu-west-1
Europe (London)eu-west-2
Europe (Frankfurt)eu-central-1
Europe (Milan)eu-south-1
Europe (Paris)eu-west-3
Europe (Stockholm)eu-north-1
US East (Ohio)us-east-2
US East (N. Virginia)us-east-1
US West (N. California)us-west-1
US West (Oregon)us-west-2
Canada (Central)ca-central-1
Africa (Cape Town)af-south-1
Asia Pacific (Hong Kong)ap-east-1
Asia Pacific (Mumbai)ap-south-1
Asia Pacific (Osaka-Local)ap-northeast-3
Asia Pacific (Seoul)ap-northeast-2
Asia Pacific (Singapore)ap-southeast-1
Asia Pacific (Sydney)ap-southeast-2
Asia Pacific (Tokyo)ap-northeast-1
China (Beijing)cn-north-1
China (Ningxia)cn-northwest-1
Middle East (Bahrain)me-south-1
South America (São Paulo)sa-east-1

3. Test your application

After a successful deployment, some information about the stack will be printed to the console (URLs of the deployed services, links to logs, metrics, etc.).

  • This project includes a pre-made test script that creates 100 websocket connections and emits a message to all of them. To run it, use


stacktape script:run --scriptName broadcastTest --stage <<your-previously-deployed-stage>> --region <<your-previously-used-region>>

4. Run the application in development mode

To run a container in the development mode (locally on your machine), you can use the dev command.


stp dev --region <<your-region>> --stage <<stage>> --resourceName websocketServer --container socketio-server

Stacktape runs the container as closely to the deployed version as possible:

  • Maps all of the container ports specified in the events section to the host machine.
  • Injects parameters referenced in the environment variables by $ResourceParam and $Secret directives to the running container.
  • Injects credentials of the assumed role to the container. This means that your locally running container will have the exact same IAM permissions as the deployed version.
  • Pretty-prints logs (stdout/stderr) produced by the container to the terminal.

The container is rebuilt and restarted, when you either:

  • type rs + enter to the terminal
  • use the --watch option and one of your source code files changes

5. Hotswap deploys

  • Stacktape deployments use AWS CloudFormation under the hood. It brings a lot of guarantees and convenience, but can be slow for certain use-cases.

  • To speed up the deployment, you can use the --hotSwap flag that avoids Cloudformation.

  • Hotswap deployments work only for source code changes (for lambda function, containers and batch jobs) and for content uploads to buckets.

  • If the update deployment is not hot-swappable, Stacktape will automatically fall back to using a Cloudformation deployment.


stacktape deploy --hotSwap --stage <<stage>> --region <<region>>

6. Delete your stack

  • If you no longer want to use your stack, you can delete it.
  • Stacktape will automatically delete every infrastructure resource and deployment artifact associated with your stack.


stp delete --stage <<stage>> --region <<region>>

Stack description

Stacktape uses a simple stacktape.yml configuration file to describe infrastructure resources, packaging, deployment pipeline and other aspects of your services.

You can deploy your services to multiple environments (stages) - for example production, staging or dev-john. A stack is a running instance of a service. It consists of your application code (if any) and the infrastructure resources required to run it.

The configuration for this service is described below.

1. Service name

You can choose an arbitrary name for your service. The name of the stack will be constructed as {service-name}-{stage}.


serviceName: socketio-websocket-api-redis

2. Resources

  • Every resource must have an arbitrary, alphanumeric name (A-z0-9).
  • Stacktape resources consist of multiple (sometimes more than 15) underlying AWS or 3rd party resources.

2.1 Application load balancer

The application load balancer is responsible for maintaining and balancing websocket connections established between clients and the containers.

If there are multiple containers(i.e your workload scales) load balancer distributes connections evenly among these containers.

You can configure more properties on your load balancer, including using custom domain names or enabling TLS. In this example, we are using the default setup.


type: application-load-balancer

2.2 Upstash Redis database

The application uses Upstash serverless Redis database. It is used by Socket.IO adapter to synchronize when scaling to multiple Socket.IO container instances.

In this example, we are configuring redis to use tls. You can also configure other properties if desired.


type: upstash-redis
enableTls: true

2.3 Container workload

Socket.IO server runs inside a container workload with a single container. The workload is configured as follows:

  • Container. This container workload uses only a single container: socketio-server. The container is configured as follows:
    • Packaging - determines how the Docker container image is built. The easiest and most optimized way to build the image for a Typescript application is using stacktape-image-buildpack. We only need to configure entryfilePath. Stacktape automatically transpiles and builds the application code with all of its dependencies, builds the Docker image, and pushes it to a pre-created image repository on AWS. You can also use other types of packaging.
    • Redis URL - we are passing it to the container as an environment variable. Redis URL connection string can be easily referenced using a $ResourceParam() directive. This directive accepts a resource name (redis in this case) and the name of the upstash redis referenceable parameter (redisUrl in this case). If you want to learn more, refer to referencing parameters guide and directives guide.
    • Events that reach the container. Load balancer event is configured to forward all incoming connections with path /(used for load balancer healthcheck) or /websockets*(used for websocket connection) to the container's port 3000.
  • Resources. Resources are shared between containers of container workload (in this case, we only have one container). The cheapest available resource configuration is 0.25 of virtual CPU and 512 MB of RAM.
  • Scaling. For the purposes of this tutorial we are scaling the workload to two (parallel) instances, to showcase the "synchronization" through redis. I.e that all websocket clients receive messages even if they are connected to different containers.


type: container-workload
cpu: 0.25
memory: 512
- name: socketio-server
type: stacktape-image-buildpack
entryfilePath: src/server/index.ts
- name: REDIS_URL
value: $ResourceParam('redis', 'redisUrl')
- name: PORT
value: 3000
- type: application-load-balancer
containerPort: 3000
loadBalancerName: mainLoadBalancer
priority: 2
- '/'
- '/websockets*'
minInstances: 2
maxInstances: 2

3. Test script

To simplify testing of the websocket app, the stacktape config also contains broadcastTest script.

The purpose of this script is to create multiple websocket client connections (connections are balanced between the 2 containers):

  • One of the clients sends a message.
  • After rest of the websockets receive the message, they gracefully disconnect and script exits.


executeScript: scripts/broadcast-test.ts
value: $ResourceParam('loadBalancer', 'domain')

You can execute the test script after the deploy using


stp script:run --scriptName broadcastTet --stage <<previously-used-stage>> --region <<previously-used-region>>
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