Zappa

Serverless Python Web Services

3 years after

Zappa Rocks!

Zappa - Serverless Python Web Services

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Zappa makes it super easy to deploy all Python WSGI applications on AWS Lambda + API Gateway. Think of it as "serverless" web hosting for your Python web apps.

What do you mean "serverless"?

Okay, so there still is a server - but it only has a 40 millisecond life cycle! Serverless in this case means "without any permanent infrastucture."

With a traditional HTTP server, the server is online 24/7, processing requests one by one as they come in. If the queue of incoming requests grows too large, some requests will time out. With Zappa, each request is given its own virtual HTTP "server" by Amazon API Gateway. AWS handles the horizontal scaling automatically, so no requests ever time out. Each request then calls your application from a memory cache in AWS Lambda and returns the response via Python's WSGI interface. After your app returns, the "server" dies.

Better still, with Zappa you only pay for the milliseconds of server time that you use, so it's many orders of magnitude cheaper than VPS/PaaS hosts like Linode or Heroku - and in most cases, it's completely free. Plus, there's no need to worry about load balancing or keeping servers online ever again.

It's great for deploying serverless microservices with frameworks like Flask and Bottle, and for hosting larger web apps and CMSes with Django. Or, you can use any WSGI-compatible app you like! You probably don't need to change your existing applications to use it, and you're not locked into using it.

And finally, Zappa is super easy to use. You can deploy your application with a single command out of the box.

Using Zappa means:

  • No more tedious web server configuration!
  • No more paying for 24/7 server uptime!
  • No more worrying about load balancing / scalability!
  • No more worrying about keeping servers online!

Awesome!

Zappa Demo Gif

Installation and Configuration

Before you begin, make sure you have a valid AWS account and your AWS credentials file is properly installed.

Zappa can easily be installed through pip, like so:

$ pip install zappa

Please note that Zappa must be installed into your project's virtual environment.

_(If you use pyenv and love to manage virtualenvs with pyenv-virtualenv, you just have to call pyenv local [your_venv_name] and it's ready. Conda users should comment here.)_

If you're looking for Django-specific integration, you should probably check out django-zappa instead.

Next, you'll need to define your local and server-side settings.

Settings

Next, you'll need to define a few settings for your Zappa deployment environments in a file named zappa_settings.json in your project directory. The simplest example is:

{
    "dev": { // The name of your environment
       "s3_bucket": "lmbda", // The name of your S3 bucket
       "app_function": "your_module.app" // The python path to your WSGI application function. In Flask, this is your 'app' object.
    }
}

You can define as many environments as your like - we recommend having dev, staging, and production.

Now, you're ready to deploy!

Basic Usage

Initial Deployments

Once your settings are configured, you can package and deploy your application to an environment called "production" with a single command:

$ zappa deploy production
Deploying..
Your application is now live at: https://7k6anj0k99.execute-api.us-east-1.amazonaws.com/production

And now your app is live! How cool is that?!

To explain what's going on, when you call deploy, Zappa will automatically package up your application and local virtual environment into a Lambda-compatible archive, replace any dependencies with versions precompiled for Lambda, set up the function handler and necessary WSGI Middleware, upload the archive to S3, register it as a new Lambda function, create a new API Gateway resource, create WSGI-compatible routes for it, link it to the new Lambda function, and finally delete the archive from your S3 bucket. Handy!

Updates

If your application has already been deployed and you only need to upload new Python code, but not touch the underlying routes, you can simply:

$ zappa update production
Updating..
Your application is now live at: https://7k6anj0k99.execute-api.us-east-1.amazonaws.com/production

This creates a new archive, uploads it to S3 and updates the Lambda function to use the new code, but doesn't touch the API Gateway routes.

Rollback

You can also rollback the deployed code to a previous version by supplying the number of revisions to return to. For instance, to rollback to the version deployed 3 versions ago:

$ zappa rollback production -n 3

Scheduling

Zappa can be used to easily schedule functions to occur on regular intervals. Just list your functions and the expression to schedule them using cron or rate syntax in your zappa_settings.json file:

{
    "dev": {
       ...
       "events": [{
           "function": "your_module.your_function", // The function to execute
           "expression": "rate(1 minute)" // When to execute it (in cron or rate format)
       }],
       ...
    }
}

And then:

$ zappa schedule production

And now your function will execute every minute!

If you want to cancel these, you can simply use the unschedule command:

$ zappa unschedule production

And now your scheduled event rules are deleted.

Undeploy

If you need to remove the API Gateway and Lambda function that you have previously published, you can simply:

$ zappa undeploy production

You will be asked for confirmation before it executes.

Tailing Logs

You can watch the logs of a deployment by calling the tail management command.

$ zappa tail production

Remote Function Invocation

You can execute any function in your application directly at any time by using the invoke command.

For instance, suppose you have a basic application in a file called "my_app.py", and you want to invoke a function in it called "my_function". Once your application is deployed, you can invoke that function at any time by calling:

$ zappa invoke production 'my_app.my_function'

Any remote print statements made and the value the function returned will then be printed to your local console. Nifty!

Django Management Commands

As a convenience, Zappa can also invoke remote Django 'manage.py' commands with the manage command. For instance, to perform the basic Django status check:

$ zappa manage production check

Obviously, this only works for Django projects which have their settings properly defined. (Please note that commands which take over 30 seconds to execute may time-out. See this related issue for a work-around.)

Advanced Usage

There are other settings that you can define in your local settings to change Zappa's behavior. Use these at your own risk!

 {
    "dev": {
        "assume_policy": "my_assume_policy.json", // optional, IAM assume policy JSON file
        "attach_policy": "my_attach_policy.json", // optional, IAM attach policy JSON file
        "aws_region": "us-east-1", // AWS Region (default US East),
        "callbacks": { // Call custom functions during the local Zappa deployment/update process
            "settings": "my_app.settings_callback", // After loading the settings
            "zip": "my_app.zip_callback", // After creating the package
            "post": "my_app.post_callback", // After command has excuted
        },
        "cache_cluster_enabled": false, // Use APIGW cache cluster (default False)
        "cache_cluster_size": .5, // APIGW Cache Cluster size (default 0.5)
        "debug": true, // Print Zappa configuration errors tracebacks in the 500
        "delete_zip": true, // Delete the local zip archive after code updates
        "django_settings": "your_project.production_settings", // The modular path to your Django project's settings. For Django projects only.
        "domain": "yourapp.yourdomain.com", // Required if you're using a domain
        "events": [{
            "function": "your_module.your_function", // The function to execute
            "expression": "rate(1 minute)" // When to execute it (in cron or rate format)
        }],
        "exclude": ["*.gz", "*.rar"], // A list of regex patterns to exclude from the archive
        "http_methods": ["GET", "POST"], // HTTP Methods to route,
        "integration_response_codes": [200, 301, 404, 500], // Integration response status codes to route
        "keep_warm": true, // Create CloudWatch events to keep the server warm.
        "lambda_handler": "your_custom_handler", // The name of Lambda handler. Default: handler.lambda_handler
        "log_level": "DEBUG", // Set the Zappa log level. Default INFO, can be one of CRITICAL, ERROR, WARNING, INFO and DEBUG.
        "memory_size": 512, // Lambda function memory in MB
        "method_response_codes": [200, 301, 404, 500], // Method response status codes to route
        "parameter_depth": 10, // Size of URL depth to route. Defaults to 8.
        "prebuild_script": "your_module.your_function", // Function to execute before uploading code
        "profile_name": "your-profile-name", // AWS profile credentials to use. Default 'default'.
        "project_name": "MyProject", // The name of the project as it appears on AWS. Defaults to a slugified `pwd`.
        "remote_env_bucket": "my-project-config-files", // optional s3 bucket where remote_env_file can be located.
        "remote_env_file": "filename.json", // file in remote_env_bucket containing a flat json object which will be used to set custom environment variables.
        "role_name": "MyLambdaRole", // Lambda execution Role
        "s3_bucket": "dev-bucket", // Zappa zip bucket,
        "settings_file": "~/Projects/MyApp/settings/dev_settings.py", // Server side settings file location,
        "timeout_seconds": 30, // Maximum lifespan for the Lambda function (default 30)
        "touch": false, // GET the production URL upon initial deployment (default True)
        "use_precompiled_packages": false, // If possible, use C-extension packages which have been pre-compiled for AWS Lambda
        "use_apigateway": true, // Set to false if you don't want to create API Gateway resource. Default true
        "vpc_config": { // Optional VPC configuration for Lambda function
            "SubnetIds": [ "subnet-12345678" ], // Note: not all availability zones support Lambda!
            "SecurityGroupIds": [ "sg-12345678" ]
        }
    }
}

Keeping The Server Warm

Zappa will automatically set up a regularly occuring execution of your application in order to keep the Lambda function warm. This can be disabled via the 'keep_warm' setting.

Enabling CORS

To enable Cross-Origin Resource Sharing (CORS) for your application, follow the AWS "How to CORS" Guide to enable CORS via the API Gateway Console. Don't forget to enable CORS per parameter and re-deploy your API after making the changes!

Deploying to a Domain With a Let's Encrypt Certificate

If you want to use Zappa on a domain with a free Let's Encrypt certificate, you can follow this guide.

Setting Environment Variables

If you want to use environment variables to configure your application (which is especially useful for things like sensitive credentials), you can create a file and place it in an S3 bucket to which your Zappa application has access to. To do this, add the remote_env_bucket and remote_env_file keys to zappa_settings pointing to a file containing a flat JSON object, so that each key-value pair on the object will be set as an environment variable and value whenever a new lambda instance spins up.

For example, to ensure your application has access to the database credentials without storing them in your version control, you can add a file to S3 with the connection string and load it into the lambda environment using the remote_env_bucket and remote_env_file configuration settings.

super-secret-config.json (uploaded to my-config-bucket):

{
    "DB_CONNECTION_STRING": "super-secret:database"
}

zappa_settings.json:

{
    "dev": {
        ...
        "remote_env_bucket": "my-config-bucket",
        "remote_env_file": "super-secret-config.json"
    },
    ...
}

Now in your application you can use:

import os
db_string = os.environ('DB_CONNECTION_STRING')

Zappa Guides

Zappa in the Press

Sites Using Zappa

Hacks

Zappa goes quite far beyond what Lambda and API Gateway were ever intended to handle. As a result, there are quite a few hacks in here that allow it to work. Some of those include, but aren't limited to..

  • Using VTL to map body, headers, method, params and query strings into JSON, and then turning that into valid WSGI.
  • Attaching response codes to response bodies, Base64 encoding the whole thing, using that as a regex to route the response code, decoding the body in VTL, and mapping the response body to that.
  • Packing and Base58 encoding multiple cookies into a single cookie because we can only map one kind.
  • Turning cookie-setting 301/302 responses into 200 responses with HTML redirects, because we have no way to set headers on redirects.

Contributing

This project is still young, so there is still plenty to be done. Contributions are more than welcome! Please file tickets before submitting patches, and submit your patches to the "dev" branch.

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