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go-zaloa

Serves Terrain tiles using the Mapzen terrain tiles with more complex shapes. Zaloa supports 256x256, 512x512, 260x260, and 516x516 pixel tiles. The source tiles are 256x256 pixels, so Zaloa fetches multiple tiles and stitches them together to get the other tile sizes.

This is a port of the Python zaloa to Go.

Deploying as AWS Lambda

Zaloa can be deployed as a Lambda to AWS. To do this:

Compile Binary

I'm running on an M1 Mac, so I need to install a cross compiler to generate the binary we'll send to AWS Lambda. This step is unnecessary if you can compile on an amd64 Linux machine:

brew install filosottile/musl-cross/musl-cross

Once your system is set up to compile to amd64+linux, compile the cmd/lambda.go file into a binary (the CC, CXX, and CGO_LDFLAGS might not be necessary if you're not on a M1 Mac):

CGO_ENABLED=1 \
GOOS=linux \
CC=x86_64-linux-musl-gcc \
CXX=x86_64-linux-musl-g++ \
CGO_LDFLAGS="-static" \
go build -o output cmd/lambda/main.go

You'll end up with a file called output that is the compiled Zaloa binary.

Package the Binary

The AWS Lambda APIs expect the binary in a .zip file, so package it like so:

zip -j output output.zip

You should have a file called output.zip that is about half the size of your output binary.

Create a Lambda Execution Role

Your Lambda will execute in AWS with a role. You use this role to specify what permissions it has. In this case, since the elevation tiles are public, our policy can be blank, but it still needs to exist. Create one using the policy JSON in this repository using the aws CLI:

aws iam create-role \
  --role-name lambda-function-executor \
  --assume-role-policy-document file://./trust-policy.json

Let's attach the built-in basic Lambda execution policy to this role you just created:

aws iam attach-role-policy \
  --role-name lambda-function-executor \
  --policy-arn arn:aws:iam::aws:policy/service-role/AWSLambdaBasicExecutionRole

Create the Lambda

Now that the role is created, you need to upload the binary and create the lambda.

Note: You must replace arn:aws:iam::1234567:role/lambda-function-executor in my example here with the ARN of the role (named lambda-function-executor) you created above.

AWS_DEFAULT_REGION=us-east-1 \
aws lambda create-function \
  --function-name zaloa \
  --runtime go1.x \
  --role="arn:aws:iam::1234567:role/lambda-function-executor" \
  --handler main \
  --zip-file fileb://./output.zip

Generate a URL

Now that your Lambda exists in AWS, you need a way to execute it and get the results into your browser. You might consider API Gateway if you need access control or tighter integration with custom domains and don't mind spending a little bit more per request. If you don't care about that because you're just using it for yourself, you can use a Lambda Function URL instead.

You can create one with a single AWS CLI command:

aws lambda create-function-url-config \
  --function-name="zaloa" \
  --auth-type="NONE"

This will return a URL with an on.aws suffix. Put that in your browser with a /tilezen/terrain/v2/512/terrarium/0/0/0.png suffix and you should get an image displayed in your browser.

Viewing Logs

You can view logs for your Lambda by logging into the AWS console, browsing to the CloudWatch Logs section, and opening the "zaloa" logging group.

Updating Code

To update to a newer version of Zaloa, you need to rebuild the binary, zip it up again, and then update the code for your Lambda with the new zipped binary:

aws lambda update-function-code \
  --function-name zaloa \
  --zip-file fileb://./output.zip