tilestrata-proxy

A TileStrata plugin for proxying tile requests. Commonly this is needed when you have a beefy vector tile server, and want rendering to happen on cheaper, more-lightweight boxes for scaling purposes.

Sample Usage

var tilestrata = require('tilestrata');
var vtileraster = require('tilestrata-vtile-raster');
var proxy = require('tilestrata-proxy');
var strata = tilestrata();

// route that proxies from an upstream server
strata.layer('vtiles').route('t.pbf').use(proxy({
	uri: 'http://domain.com/{z}/{x}/{y}.mvt',
}));

// rasterize the vector tiles
strata.layer('mylayer').route('t.png').use(vtileraster({
		xml: '/home/ybon/Code/maps/thankyou/mapnik.xml',
		tileSize: 256,
		metatile: 1,
		bufferSize: 128,
		tilesource: ['vtiles', 't.pbf']
}));

strata.listen(8080);

The plugin will automatically decompress gzipped content by default regardless of the client's Accept-Encoding header. This is due to the fact that proxied content is often used as part of a pipeline (it's not served directly to the client). This isn't always the case though. Decompression behavior is configurable:

// always decompress gzipped content
proxy({ decompress: 'always' });

// decompress only if the client does not support compression
proxy({ decompress: 'client' });

// never decompress gzipped content
proxy({ decompress: 'never' });

To specify custom request headers, use the headers option:

proxy({
	uri: '...',
	headers: {
		'User-Agent': 'TileStrata/' + tilestrata.version
	}
})

Retries

By default, failed requests will not cause a retry to be attempted. To enable retries, set the retries option to the number of retries you want to allow. Retries will be delayed with exponential backoff with sane defaults.

proxy({ retries: 5 });

To tune exponential backoff, set the following options:

proxy({
	// total number of retries
	retries: 5,
	// initial delay (ms)
	retryDelayBase: 500,
	// exponent base
	retryDelayMultiple: 1.75,
	// max delay (ms)
	retryDelayMax: 60000,
});

The delay is computed as:

delay = min(retryDelayMax, retryDelayBase * Math.pow(retryDelayMultiple, retryNumber))

Other Options

// spread requests across different subdomains ala leaflet
.use(proxy({
	uri: 'http://{s}.domain.com/{z}/{x}/{y}.png',
	subdomains: 'abc',
}));

.use(proxy({
	uri: 'http://{s}.domain.com/{z}/{x}/{y}.png',
	subdomains: ['a', 'b', 'c'],
}));

// request arbitrary urls
.use(proxy({
	uri: tile => {
		// note: if you return a falsy value this will cause a 404 Not Found to be returned
		return 'http://domain.com/' + tile.z + '/' + tile.x + '/' + tile.y + '.png';
	},
}));

Contributing

Before submitting pull requests, please update the tests and make sure they all pass.

$ npm test

License

Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at: http://www.apache.org/licenses/LICENSE-2.0