Overview

• Web service is a computing resource - it runs your code. Web service runs continuously and scales based on the CPU and RAM usage.

• Web service has a publicly accessible HTTPS URL endpoint for routing traffic to the service container (Only HTTPS requests (port 443) are accepted).

• Similarly to functions and batch jobs, web services are serverless and fully managed. This means you don't have to worry about administration tasks such as provisioning and managing servers, scaling, VM security, OS security & much more.

• The container image can be supplied in 3 different ways:

  • built automatically from your source code by Stacktape
  • built using a supplied Dockerfile by Stacktape
  • pre-built images

• Web services run securely within a Virtual Private Cloud (VPC).

When to use

Advantages

• Control over underlying environment - Web service can run any Docker image or image built using your own Dockerfile.
• Price for workloads with predictable load - Compared to functions, web services are cheaper if your workload has a predictable load.
• Load-balanced and auto-scalable - Web services can automatically horizontally scale based on the CPU and Memory utilization.
• High availability - Web services run in multiple Availability Zones.
• Secure by default - Underlying environment is securely managed by AWS.

Disadvantages

• Scaling speed - Unlike lambda functions that scale almost instantly, web service requires more time - from several seconds to few minutes to add another container.

• Not fully serverless - While web services can automatically scale up and down, they can't scale to 0. This means, if your workload is unused, you are still paying for at least one instance (minimum ~$8/month)

Basic usage

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import express from 'express';

const app = express();

app.get('/', async (req, res) => {
  res.send({ message: 'Hello' });
});

// for your use port number stored in PORT environment variable for your application
// this environment variable is automatically injected by Stacktape
app.listen(process.env.PORT, () => {
  console.info(`Server running on port ${process.env.PORT}`);
});

YAML
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resources:
  webService:
    type: web-service
    properties:
      packaging:
        type: stacktape-image-buildpack
        properties:
          entryfilePath: src/main.ts
      resources:
        cpu: 2
        memory: 2048

Image

• Web Service is a running instance of a Docker image.
• The image of the container can be supplied in 4 different ways:
  • images built using stacktape-image-buildpack
  • images built using external-buildpack
  • images built from the custom-dockerfile
  • prebuilt-images

Environment variables

YAML
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resources:
  webService:
    type: web-service
    properties:
      packaging:
        type: stacktape-image-buildpack
        properties:
          entryfilePath: src/main.ts
      environment:
        - name: STATIC_ENV_VAR
          value: my-env-var
        - name: DYNAMICALLY_SET_ENV_VAR
          value: $MyCustomDirective('input-for-my-directive')
        - name: DB_HOST
          value: $ResourceParam('myDatabase', 'host')
        - name: DB_PASSWORD
          value: $Secret('dbSecret.password')
      resources:
        cpu: 2
        memory: 2048

Healthcheck

The purpose of the container health check is to monitor the health of the container from the inside.

Once an essential container of an instance is determined UNHEALTHY, the instance is automatically replaced with a new one.

• Example: A shell command sends a curl request every 20 seconds to determine if the service is available. If the request fails (or doesn't return in 5 seconds), the command returns with non-zero exit code, and the healtcheck is considered failed.

YAML
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resources:
  myWebService:
    type: web-service
    properties:
      packaging:
        type: stacktape-image-buildpack
        properties:
          entryfilePath: src/index.ts
      internalHealthCheck:
        healthCheckCommand: ['CMD-SHELL', 'curl -f http://localhost/ || exit 1']
        intervalSeconds: 20
        timeoutSeconds: 5
        startPeriodSeconds: 150
        retries: 2
      resources:
        cpu: 2
        memory: 2048

Shutdown

• When a running web service instance is deregistered (removed), all running containers receive a SIGTERM signal.
• You then have 30 seconds to clean up. After 30 seconds, your process recives a SIGKILL signal.

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process.on('SIGTERM', () => {
  console.info('Received SIGTERM signal. Cleaning up and exiting process...');

  // Finish any outstanding requests, or close a database connection...

  process.exit(0);
});

Logging

• Every time your code outputs (prints) something to the stdout or stderr, your log will be captured and stored in a AWS CloudWatch log group.
• You can browse your logs in 2 ways:
  • go to your web service's log-group in the AWS CloudWatch console. You can use stacktape stack-info command to get a direct link.
  • use stacktape logs command that will print logs to the console

Resources

• You must configure computing resources (CPU and RAM) for your web service.
• Configured resources are valid for every container instance in the web service (if there are more than 1 instance running).

YAML
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resources:
  myWebService:
    type: web-service
    properties:
      packaging:
        type: stacktape-image-buildpack
        properties:
          entryfilePath: src/index.ts
      resources:
        cpu: 0.25
        memory: 512

Scaling

• Configures scaling behavior of your web service. You can configure:
  • Initial, minimum and maximum amount of concurrently running instances in your workload.
  • Conditions which trigger the scaling (up or down) using a scaling policy.

Scaling policy

• A scaling policy specifies CPU and memory metric thresholds which trigger the scaling process.

• Depending on the thresholds, the workload can either scale out (add instances) or scale in (remove instances).

• If both keepAvgCpuUtilizationUnder and keepAvgMemoryUtilizationUnder are used, the workload will scale-out if one of the metrics is above the target value. However, to scale in, both of these metrics need to be below their respective target values.

• Scaling policy is more aggressive in adding capacity then removing capacity. For example, if the policy's specified metric reaches its target value, the policy assumes that your application is already heavily loaded. So it responds by adding capacity proportional to the metric value as fast as it can. The higher the metric, the more capacity is added.

• When the metric falls below the target value, the policy expects that utilization will eventually increase again. Therefore it slows down the scale-in process by removing capacity only when utilization passes a threshold that is far enough below the target value (usually 20% lower).

YAML
Typescript
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resources:
  myWebService:
    type: web-service
    properties:
      packaging:
        type: stacktape-image-buildpack
        properties:
          entryfilePath: src/index.ts
      resources:
        cpu: 0.5
        memory: 1024
      scaling:
        minInstances: 1
        maxInstances: 5
        scalingPolicy:
          keepAvgMemoryUtilizationUnder: 80
          keepAvgCpuUtilizationUnder: 80

Storage

• Each web service instance has access to its own ephemeral storage. It's removed after the web service instances is removed.
• It has a fixed size of 20GB.
• If you have 2 concurrently running web service intances, they do not share this storage.
• To store data persistently, consider using Buckets.

Accessing other resources

• For most of the AWS resources, resource-to-resource communication is not allowed by default. This helps to enforce security and resource isolation. Access must be explicitly granted using IAM (Identity and Access Management) permissions.

• Access control of Relational Databases is not managed by IAM. These resources are not "cloud-native" by design and have their own access control mechanism (connection string with username and password). They are accessible by default, and you don't need to grant any extra IAM permissions. You can further restrict the access to your relational databases by configuring their access control mode.

• Stacktape automatically handles IAM permissions for the underlying AWS services that it creates (i.e. granting web services permission to write logs to Cloudwatch, allowing web services to communicate with their event source and many others).

If your workload needs to communicate with other infrastructure components, you need to add permissions manually. You can do this in 2 ways:

Using allowAccessTo

• List of resource names or AWS services that this web service will be able to access (basic IAM permissions will be granted automatically). Granted permissions differ based on the resource.
• Works only for resources managed by Stacktape (not arbitrary Cloudformation resources)
• This is useful if you don't want to deal with IAM permissions yourself. Handling permissions using raw IAM role statements can be cumbersome, time-consuming and error-prone.

YAML
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resources:
  photosBucket:
    type: bucket

  myWebService:
    type: web-service
    properties:
      packaging:
        type: stacktape-image-buildpack
        properties:
          entryfilePath: src/index.ts
      accessControl:
        allowAccessTo:
          # access to the bucket
          - photosBucket
          # access to AWS SES
          - aws:ses
      resources:
        cpu: 0.25
        memory: 512

Using iamRoleStatements

• List of raw IAM role statement objects. These will be appended to the web service's role.
• Allow you to set granular control over your web service's permissions.
• Can be used to give access to any Cloudformation resource

YAML
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resources:
  myWebService:
    type: web-service
    properties:
      packaging:
        type: stacktape-image-buildpack
        properties:
          entryfilePath: server/index.ts
      accessControl:
        iamRoleStatements:
          - Resource:
              - $CfResourceParam('NotificationTopic', 'Arn')
            Effect: 'Allow'
            Action:
              - 'sns:Publish'
      resources:
        cpu: 2
        memory: 2048

cloudformationResources:
  NotificationTopic:
    Type: 'AWS::SNS::Topic'

Default VPC connection

• Certain AWS services (such as Relational Databases) must be connected to a VPC (Virtual private cloud) to be able to run. For stacks that include these resources, Stacktape does 2 things:
  • creates a default VPC
  • connects the VPC-requiring resources to the default VPC.
• web services are connected to the default VPC of your stack by default. This means that web services can communcate with resources that have their accessibility mode set to vpc without any extra configuration.
• To learn more about VPCs and accessibility modes, refer to VPC docs, accessing relational databases, accessing redis clusters and accessing MongoDb Atlas clusters.

CORS

Cross-origin resource sharing (CORS) is a browser security feature that restricts cross-origin HTTP requests that are initiated from scripts running in the browser.

A cross-origin HTTP request is a request that is made to a different domain or a different subdomain than the one browser is currently on.

Example: If your website has domain mydomain.com and it communicates with your web-service which has domain api.mydomain.com then the browser must perform cross origin request when communcating with this web-service.

There are two types of cross-origin requests:

1. Simple requests

   • requests that do not require CORS preflight.
   • To understand what is considered a simple request refer to Mozilla docs.
   • You do not need to configure CORS on your gateway for these types of requests. However, responses from your application should still include Access-Control-Allow-Origin header where the value of the header key is set to *(any origin) or is set to the origins allowed to access that resource. Refer to Mozilla docs for more information.

2. NON-simple (preflighted) requests

   • all cross origin requests that are not considered simple are NON-simple and require preflight requests.
   • If you send NON-simple CORS requests from browser to your API, you can enable CORS which takes care of preflight requests, and sets the neccessary response headers.

If you need to use NON-simple cross origin requests you need to enable CORS. CORS can be enabled with a signle line.

YAML
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resources:
  myWebService:
    type: 'web-service'
    properties:
      resources:
        cpu: 2
        memory: 2048
      packaging:
        type: stacktape-image-buildpack
        properties:
          entryfilePath: src/main.ts
      cors:
        enabled: true

You can additionally configure CORS headers by setting properties in cors configuration.

Custom domain names

YAML
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resources:
  myWebService:
    type: web-service
    properties:
      resources:
        cpu: 2
        memory: 2048
      packaging:
        type: stacktape-image-buildpack
        properties:
          entryfilePath: src/main.ts
      customDomains:
        - domainName: whatever.mydomain.com

CDN

You can configure AWS Cloudfront CDN (Content Delivery Network) to be in front of your web-service.

For information about using CDN refer to our CDN docs.

Referenceable parameters

Pricing

You are charged for:

• Virtual CPU / hour:

  • depending on the region $0.04048 - $0.0696

• Memory GB / hour:

  • depending on the region $0.004445 - $0.0076

The duration is rounded to 1 second with a 1 minute minimum. To learn more, refer to AWS Fargate pricing.

API reference