go-rasterzen-lambda

Run the go-rasterzen code in an AWS Lambda function.

IMPORTANT

This package has been deprecated and is no longer being maintained. All the functionality has been moved in to the go-rasterzen package.

Install

You will need to have both Go (specifically a version of Go more recent than 1.7 so let's just assume you need Go 1.9 or higher) and the make programs installed on your computer. Assuming you do just type:

make bin

All of this package's dependencies are bundled with the code in the vendor directory.

Important

This works, or more specifically appears to work for me so it will probably work for you too, right?

There are a couple important things to keep in mind:

• Tiles are only cached in S3
• There is still no cache invalidation logic (in go-rasterzen) so you should be ready to manually purge or otherwise investigate S3 data
• There are no hooks (in go-rasterzen) for enabling chatty logging which means introspecting any kind of errors in the Lambda function will be... "fun"

What follows is a small thumderstorm of AWS alphabet (services) soup that you'll need to power your way through to get this to work.

Lambda

aws lambda create-function --region {REGION} --function-name Rasterzen \
    --zip-file fileb://./deployment.zip --runtime go1.x --tracing-config Mode=Active \
    --role {ROLE} --handler main

See notes on (IAM) roles below

Environment variables

You will need to configure your Lamdba function to set the following environment variables:

RASTERZEN_S3_DSN

bucket={BUCKET} prefix={PREFIX} region={REGION} credentials=iam:

RASTERZEN_CACHE_OPTIONS

ACL=public-read

Or you can leave this empty if you don't want the cached tiles to be public.

Basic settings

It is unlikely that the default execution timeout settings (3 seconds) will be enough to fetch and process some tiles. You should adjust this as necessary.

IAM Roles

• AWSLambdaExecute
• AWSXRayFullAccess (I don't know why... maybe it's the tracing flag above?)
• A role that allows your function to read/write to the S3 bucket defined in RASTERZEN_S3_DSN

CloudFront

Can't be done without routing all the requests though API Gateway, yet. Apparently Lambda functions written in Go do not work as CloudFront triggers.

If you are going to use API Gateway (more below) you should make sure to read the Lambda gotchas section of the Tilezen tapalcatl-py package.

API Gateway

Okay, so this is still all a bit slippery for me, meaning I can barely ever keep track of all the buttons you have to press to accomplish things in AWS. It's very possible, still, that I've missed something or gotten something else wrong. Gentle cluebats are welcome and encouraged.

• Once you've created your API, you want to "Create Resource" from the Actions menu.
• Configure it as a proxy resource
• Set the Resource Name to be "/" (or whatever you need it to be)
• Set the Resource Path to be "{proxy+}" (... I have no idea what's going on here)
• Enable the CORS gateway if you want...

Really important

In order for requests to produce PNG output (rather than a base64 encoded string) you will need to do a few things:

1. Make sure your API Gateway settings list image/png as a known and valid binary type:

2. If you've put a CloudFront distribution in front of your API Gateway then you will to ensure that you blanket enable all HTTP headers or whitelist the Accept: header , via the Cache Based on Selected Request Headers option (for the CloudFront behaviour that points to your gateway):

3. Make sure you pass an Accept: image/png header when you request the PNG rendering.

Testing

In the Method menu select

• GET

In the Path {proxy} field add something like:

• /svg/13/1315/3171.json

And in the `Query Strings {proxy} field add:

• api_key={NEXTZEN_APIKEY}

In principle at this point you should get back a 200 OK response and there should be tiles in your S3 bucket. If it doesn't then... uh... AWS???

See also

Package specific

• https://github.com/whosonfirst/go-rasterzen
• https://github.com/whosonfirst/go-whosonfirst-aws
• https://artem.krylysov.com/blog/2018/01/18/porting-go-web-applications-to-aws-lambda/
• https://github.com/akrylysov/algnhsa

AWS

• https://aws.amazon.com/blogs/compute/announcing-go-support-for-aws-lambda/
• https://docs.aws.amazon.com/lambda/latest/dg/lambda-go-how-to-create-deployment-package.html
• https://docs.aws.amazon.com/lambda/latest/dg/env_variables.html
• https://docs.aws.amazon.com/cli/latest/reference/sts/get-session-token.html

General

• https://apimeister.com/2017/05/09/hosting-a-cloudfront-site-with-s3-and-api-gateway.html
• https://github.com/tilezen/tapalcatl-py#lambda-gotchas