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aleksplus / tilestrata

A pluggable Node.js map tile server.

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TileStrata

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TileStrata is a pluggable "slippy map" tile server that emphasizes code-as-configuration. It's clean, highly tested, and performant. After using TileStache (excellent) we decided we needed something that more-closely matched our stack: Node.js. The primary goal is painless extendability. This fork uses different url scheme in routes

$ npm install tilestrata --save

Introduction

TileStrata consists of five main actors, usually implemented as plugins:

  • "provider" – Generates a new tile (e.g mapnik)
  • "cache" – Persists a tile for later requests (e.g. filesystem)
  • "transform" – Takes a raw tile and transforms it (e.g. image scaling / compression)
  • "request hook" – Called at the very beginning of a tile request.
  • "response hook" – Called right before a tile is served to the client.

List of Plugins

Configuration

var tilestrata = require('tilestrata');
var disk = require('tilestrata-disk');
var sharp = require('tilestrata-sharp');
var mapnik = require('tilestrata-mapnik');
var dependency = require('tilestrata-dependency');
var strata = tilestrata.createServer();

// define layers
strata.layer('basemap')
    .route('@2x.png')
        .use(disk.cache({dir: '/var/lib/tiles/basemap'}))
        .use(mapnik({
            xml: '/path/to/map.xml',
            tileSize: 512,
            scale: 2
        }))
    .route('.png')
        .use(disk.cache({dir: '/var/lib/tiles/basemap'}))
        .use(dependency('basemap', 'tile@2x.png'))
        .use(sharp(function(image, sharp) {
            return image.resize(256);
        }));

// start accepting requests
strata.listen(8080);

Once configured and started, tiles can be accessed via:

/:layer/:z/:x:/:filename

Integrate with Express.js / Connect

TileStrata comes with middleware for Express that makes serving tiles from an existing application really simple, eliminating the need to call listen on strata.

var tilestrata = require('tilestrata');
var strata = tilestrata.createServer();
strata.layer('basemap') /* ... */
strata.layer('contours') /* ... */

app.use(tilestrata.middleware({
    server: strata,
    prefix: '/maps'
}));

Usage Notes

Rebuilding the Tile Cache

If you update your map styles or data, you'll probably want to update your tiles. Rather than dump of them at once and bring your tile server to a crawl, progressively rebuild the cache by requesting tiles with the X-TileStrata-SkipCache header. TileMantle makes this process easy:

npm install -g tilemantle
tilemantle http://myhost.com/mylayer/{z}/{x}/{y}/t.png \
    -p 44.9457507,-109.5939822 -b 30mi -z 10-14 \
    -H "X-TileStrata-SkipCache:mylayer/t.png"

For the sake of the tilestrata-dependency plugin, the value of the header is expected to be in the format:

X-TileStrata-SkipCache:*
X-TileStrata-SkipCache:[layer]/[file],[layer]/[file],...

In advanced use cases, it might be necessary for tiles to not be returned by the server until the cache is actually written (particularly when order matters due to dependencies). To achieve this, use:

X-TileStrata-CacheWait:1

Health Checks

TileStrata includes a /health endpoint that will return a 200 OK if it can accept connections. The response will always be JSON. By setting strata.healthy to a function that accepts a callback you can take it a step further and control the status and data that it returns.

// not healthy
strata.healthy = function(callback) {
    callback(new Error('CPU is too high'), {loadavg: 3});
};
// healthy
strata.healthy = function(callback) {
    callback(null, {loadavg: 1});
};

Profiling / Debugging Performance

Unless the TILESTRATA_NOPROFILE environment variable is set, TileStrata keeps track of basic latency and size information (min, max, avg) for all steps in the tile serving flow for the lifetime of the process. Data is kept for every plugin on every route of every layer and is broken down by zoom level. To access it, visit: /profile in your browser. If this information needs to be kept private, you can set the TILESTRATA_PASSWORD environment variable to a password that TileStrata will prompt for (username is ignored). The page will have tables like the one below:

t.pngz1z2z3z4z5z6z7z8z9
reqhook#0errors000000000
dur_samples112111111
dur_max454443465250586181
dur_min454442465250586181
dur_avg454442.5465250586181
cache#0.geterrors000000000
dur_samples112111111
dur_max454544584762466053
dur_min454544584762466053
dur_avg454544584762466053
hits000000000
misses112111111
provider#0errors000000000
dur_samples112111111
dur_max344396122119108115103129
dur_min344364122119108115103129
dur_avg344380122119108115103129
size_samples112111111
size_max500B501B576B578B504B540B501B776B736B
size_min500B501B565B578B504B540B501B776B736B
size_avg500B501B571B578B504B540B501B776B736B
transform#0errors000000000
dur_samples112111111
dur_max323335614957535069
dur_min323334614957535069
dur_avg323334.5614957535069
reshook#0errors000000000
dur_samples112111111
dur_max454345636355486068
dur_min454344636355486068
dur_avg454344.5636355486068
cache#0.seterrors000000000
dur_samples112111111
dur_max121313142723262927
dur_min121310142723262927
dur_avg121311.5142723262927

API Reference

TileServer

server.listen(port, [hostname], [callback])

Starts accepting requests on the specified port. The arguments to this method are exactly identical to node's http.Server listen() method.

server.layer(name, [opts])

Registers a new layer with the given name and returns its TileLayer instance. If the layer already exists, the existing instance will be returned. Whatever name is used will be the first part of the url that can be used to fetch tiles: /:layer/.... The following options can be provided:

  • bbox: A bounding box (GeoJSON "bbox" format) that defines the valid extent of the layer. Any requests for tiles outside of this region will result in a 404 Not Found. This option can also be set to an array of bounding boxes for rare cases when a layer is noncontinuous.
  • minZoom: The minimum z to return tiles for. Anything lesser will return a 404 Not Found.
  • maxZoom: The maximum z to return tiles for. Anything greater will return a 404 Not Found.
server.getTile(layer, filename, x, y, z, callback)

Attempts to retrieve a tile from the specified layer (string). The callback will be invoked with three arguments: err, buffer, and headers.

server.version

The version of TileStrata (useful to plugins, mainly).

TileLayer

layer.route(filename, [options])

Registers a route. Returns a TileRequestHandler instance to be configured. The available options are:

  • cacheFetchMode: Defines how cache fetching happens when multiple caches are configured. The mode can be "sequential" or "race". If set to "race", TileStrata will fetch from all caches simultaneously and return the first that wins.

TileRequestHandler

handler.use(plugin)

Registers a plugin, which is either a provider, cache, transform, request hook, response hook, or combination of them. See the READMEs on the prebuilt plugins and/or the "Writing TileStrata Plugins" section below for more info.

TileRequest

A request contains these properties: x, y, z, layer (string), filename, method, headers, and qs.

tile.clone()

Returns an identical copy of the tile request that's safe to mutate.

Writing TileStrata Plugins

Writing Request Hooks

A request hook implementation needs one method: reqhook. Optionally it can include an init method that gets called when the server is initializing. The hook's "req" will be a http.IncomingMessage and "res" will be the http.ServerResponse. This makes it possible to respond without even getting to the tile-serving logic (just don't call the callback).

module.exports = function(options) {
    return {
        init: function(server, callback) {
            callback(err);
        },
        reqhook: function(server, tile, req, res, callback) {
            callback();
        }
    };
};

Writing Caches

A cache implementation needs two methods: get, set. Optionally a cache can declare an init method that gets called when the server is initializing. If a cache fails (returns an error to the callback), the server will ignore the error and attempt to serve the tile from the registered provider.

module.exports = function(options) {
    return {
        init: function(server, callback) {
            callback(err);
        },
        get: function(server, tile, callback) {
            callback(err, buffer, headers, /* refresh */);
        },
        set: function(server, tile, buffer, headers, callback) {
            callback(err);
        }
    };
};

A special behavior exists for when a cache returns a hit, but wants a new tile to be generated in the background. The use case: you have tile that's old enough it should be regenerated, but it's not old enough to warrant making the user wait for a new tile to be rendered. To accomplish this in a plugin, have get() return true as the fourth argument to the callback.

callback(null, buffer, headers, true);

Writing Providers

Providers are responsible for building tiles. A provider must define a serve method and optionally an init method that is called when the server starts.

module.exports = function(options) {
    return {
        init: function(server, callback) {
            callback(err);
        },
        serve: function(server, tile, callback) {
            callback(err, buffer, headers);
        }
    };
};

Writing Transforms

Transforms modify the result from a provider before it's served (and cached). A tranform must define a transform method and optionally an init method.

module.exports = function(options) {
    return {
        init: function(server, callback) {
            callback(err);
        },
        transform: function(server, tile, buffer, headers, callback) {
            callback(err, buffer, headers);
        }
    };
};

Writing Response Hooks

A response hook implementation needs one method: reshook. Optionally it can include an init method that gets called when the server is initializing. The hook's "req" will be a http.IncomingMessage and "res" will be the http.ServerResponse. The "result" argument contains three properties: headers, buffer, and status — each of which can be modified to affect the final response.

module.exports = function(options) {
    return {
        init: function(server, callback) {
            callback(err);
        },
        reshook: function(server, tile, req, res, result, callback) {
            callback();
        }
    };
};

Multi-Function Plugins

Sometimes a plugin must consist of multiple parts. For instance, a plugin tracking response times must register a request hook and response hook. To accomodate this, TileStrata supports arrays:

module.exports = function() {
    return [
        {reqhook: function(...) { /* ... */ }},
        {reshook: function(...) { /* ... */ }}
    ];
};

Contributing

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

$ npm test

License

Copyright © 2014–2015 Natural Atlas, Inc. & Contributors

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

Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.

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A pluggable Node.js map tile server.

License:Apache License 2.0

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