Serverless Added in v1.0.0

A plugin to run Eleventy in a serverless function for server side rendering (e.g. Previews in your CMS) and/or in very large sites with On-demand Builders.

What is Serverless? Jump to heading #

Eleventy Serverless complements your existing statically generated site by running one or more template files at request time to generate dynamic pages. It can unlock many new use cases to move beyond static files into dynamically generated content.

• Server side rendering for fully dynamic pages, e.g. content preview in your Content Management System.
• Rendering of individual templates using On-demand Builders, useful to improve large site build times both locally and in production.

“You can write a JavaScript function that you run and receive a response from by hitting a URL.”—The Power of Serverless from Chris Coyier

Rendering Modes Jump to heading #

These different use cases and rendering modes are important to understand and have different trade-offs and risks associated with them. In a Jamstack world, the order of preference should be:

1. Build template: Render in the build (preferred, start here)
2. On-demand Builder template: Render on first request (use when your build gets beefy)
3. Dynamic template: Render on every request (unlocks some new app-like use cases; can accept user input)

Build-time (non-serverless) templates should be the preferred rendering mode. They are the most reliable and stable. A failure in a build generated template will fail your deployment and prevent user-facing errors in production.

For On-demand Builders and Dynamic templates, rendering failures will not fail your deployment—and as such, incur more risk. Dynamic templates must also be closely performance monitored—unlike build templates, a slow render in a dynamic template means a slow web site for end-users.

Demos and Community Resources Jump to heading #

Eleventy API Explorer

• Source code
• Deploy to Netlify
• Try on StackBlitz

Eleventy Serverless Color Contrast

• Source code
• Deploy to Netlify
• Try on StackBlitz

Eleventy Serverless Demo

• Source code
• Deploy to Netlify
• Try on StackBlitz

The starter project to learn about Eleventy Serverless

Object-fit Focal Point

Rainglow

• Source code
• Deploy to Netlify
• Try on StackBlitz

Uniclode

• Source code
• Deploy to Netlify
• Try on StackBlitz

Creating a dynamic color converter with 11ty Serverless

Building A Static-First MadLib Generator With Portable Text And Netlify On-Demand Builder Functions

Building server-rendered search for static sites with 11ty Serverless, Netlify, and Algolia

A First Look at Eleventy Serverless, with Zach Leatherman

Usage Jump to heading #

Step 1: Add the Bundler Plugin Jump to heading #

This plugin is bundled with Eleventy core and doesn’t require you to npm install anything. Use the addPlugin() configuration API to add it to your Eleventy config file (probably .eleventy.js):

const { EleventyServerlessBundlerPlugin } = require("@11ty/eleventy");

module.exports = function(eleventyConfig) {
  eleventyConfig.addPlugin(EleventyServerlessBundlerPlugin, {
    name: "possum", // The serverless function name from your permalink object
    functionsDir: "./netlify/functions/",
  });
};

You can add the Bundler plugin more than once to accommodate multiple Eleventy Serverless rendering modes simultaneously. Your templates can render in multiple modes!

Bundler Options Jump to heading #

Your Generated Serverless Function Jump to heading #

Based on your plugin configuration, Eleventy will create your initial boilerplate serverless function for you. After initial creation, this serverless function code is managed by you.

Here is an over-simplified version for educational purposes only:

const { EleventyServerless } = require("@11ty/eleventy");

async function handler (event) {
  let elev = new EleventyServerless("possum", {
    path: event.path, // (required) the URL path
    query: event.queryStringParameters, // (optional)
  });

  try {
    // returns the HTML for the Eleventy template that matches to the URL
    // Can use with `eleventyConfig.dataFilterSelectors` to put data cascade data into `page.data` here.
    let [page] = await elev.getOutput();
    let html = page.content;

    return {
      statusCode: 200,
      body: html
    };
  } catch(e) {
    return {
      statusCode: 500,
      body: JSON.stringify({ error: e.message })
    };
  }
};

exports.handler = handler;

Read more about dataFilterSelectors.

Use with On-demand Builders Jump to heading #

If, instead, you want to use an On-demand Builder to render the content on first-request and cache at the CDN for later requests, you will need to do two things:

Thing 1: Swap the export in your template (and npm install @netlify/functions):

exports.handler = handler;

Replace the above with:

const { builder } = require("@netlify/functions");
exports.handler = builder(handler);

Thing 2: Use redirects: "netlify-toml-builders" in your bundler config.

The redirects need to point to /.netlify/builders/ instead of /.netlify/functions so if you have written your own redirects handler, you’ll need to update that.

Step 2: Add to .gitignore Jump to heading #

Add the following rules to your .gitignore file (where possum is the name of your serverless function name):

netlify/functions/possum/**
!netlify/functions/possum/index.js

Step 3: Use a permalink Object Jump to heading #

Making a template file dynamic is as easy as changing your permalink. You might be familiar with this well-worn permalink syntax:

---
permalink: /build-generated-path/
---

Serverless templates introduce a slight change: they use a permalink Object. So a possum serverless function permalink looks like this:

---
permalink:
  possum: /dynamic-path/
---

These objects can be set anywhere in the data cascade (even inside of Computed Data).

Here’s an example of a serverless URL for our possum serverless function. Any requests to /dynamic-path/ will now be generated at request-time.

The following is functionally equivalent to permalink: /build-generated-path/:

---
permalink:
  build: /build-generated-path/
---

Anything other than build is assumed to map to a serverless function. We used the name possum, but you can use any string. (Just make sure it maps to the name you passed to the Bundler Plugin above.)

Build-time and Serverless Jump to heading #

You can mix both build and possum in the same permalink object! This will make the same input file render both at build-time and in a serverless function.

This might be useful when you want a specific URL for a CMS preview, but still want the production build to use full build-time templates.

---
permalink:
  build: /build-generated-path/
  possum: /dynamic-path/
---

Multiple Serverless Functions Jump to heading #

Any number of serverless functions are allowed here.

---
permalink:
  possum: /dynamic-path/
  quokka: /some-other-dynamic-path/
---

Multiple URLs per Serverless Function Jump to heading #

If you want to drive multiple URLs with one serverless template, pass in an Array of URLs.

---
permalink:
  possum:
    - /dynamic-path/
    - /some-other-dynamic-path/
---

Dynamic Slugs and Serverless Global Data Jump to heading #

Perhaps most interestingly, this works with dynamic URLs, too! This will work with any syntax supported by the path-to-regexp package.

---
permalink:
  possum: /dynamic-path/:id/
---

This will match any requested URL that fits the /dynamic-path/ followed by an open-ended folder name (e.g., /dynamic-path/hello/ or /dynamic-path/goodbye/).

The above uses :id for the key name. When the templates are rendered, the key name puts the matched path String value for id into your Serverless Global Data in the Data Cascade at: eleventy.serverless.path.id. (Here, id matches :id above).

Here’s what your Serverless Global Data might look like:

{
  eleventy: {
    serverless: {
      path: {
        id: "hello" // from /dynamic-path/hello/
        //id: "goodbye" // from /dynamic-path/goodbye/
      }
    }
  }
}

Escaping User Input Jump to heading #

These should be treated as potentially malicious user input, and you must escape these if you use them in templates!
The way to do this is specific to each template language.

• Liquid has both an escape and escape_once filter.
• Nunjucks has autoescape turned on by default. (If you’ve disabled it, you can use the escape filter.)
• Other template languages: Read more in the Layouts documentation, which has other template languages’ methods for both escaped and unescaped output.

Advanced Jump to heading #

Dynamic Slugs to Subset Your Pagination Jump to heading #

Use the new serverless option in pagination to slice up your paginated data set using a dynamic slug!

Here’s how we use it for the Eleventy Author Pages.

pagination:
  data: authors
  size: 1
  serverless: eleventy.serverless.path.id
permalink:
  possum: "/authors/:id/"

Eleventy fetches the value stored at eleventy.serverless.path.id (using lodash get) and does an additional get on the pagination data in authors.

For example:

1. A request is made to /authors/zachleat/
2. The dynamic URL slug for the possum serverless function /authors/:id/ matches zachleat to :id. This sets "zachleat" in the eleventy.serverless.path.id Global Data.
3. Because pagination.serverless has the value "eleventy.serverless.path.id", we use lodash.get to select the key "zachleat" from Global Data.
4. An additional lodash.get(authors, "zachleat") returns a single chunk of data for one author.
5. Pagination only operates on that one selected page for rendering.

Input via Query Parameters Jump to heading #

In Dynamic Templates (not On-demand Builders), you can use query parameters as user input. Query parameters are available in the eleventy.serverless.query object.

/my-url/?id=hello might look like this in the Data Cascade of a dynamic template:

{
  eleventy: {
    serverless: {
      query: {
        id: "hello" // from /my-url/?id=hello
        //id: "goodbye" // from /my-url/?id=goodbye
      }
    }
  }
}

Re-use build-time cache from the Fetch plugin Jump to heading #

To speed up serverless rendering and avoid requests to external sources, you can re-use the cache folder from your build!

First, we’ll need to copy the cache folder into our bundle.

const { EleventyServerlessBundlerPlugin } = require("@11ty/eleventy");

module.exports = function(eleventyConfig) {
  eleventyConfig.addPlugin(EleventyServerlessBundlerPlugin, {
    name: "possum",
    copy: [
      ".cache/eleventy-fetch/",
    ]
  });
};

And re-use the directory in your data files:

const EleventyFetch = require("@11ty/eleventy-fetch");

module.exports = async function() {
  let options = {
    // Use the same folder declared above
    directory: ".cache/eleventy-fetch/"
  };

  if(process.env.ELEVENTY_SERVERLESS) {
    // Infinite duration (until the next build)
    options.duration = "*";

    // Bypass writing new cache files, which would error in serverless mode
    options.dryRun = true;
  }

  let result = await EleventyFetch("https://example.com/", options);
  // …
};

Collections in Serverless Jump to heading #

Eleventy Serverless typically operates on a subset of templates in your project. As such, collections that are outside the scope of the serverless build are not available in serverless mode. You have two options to workaround this limitation:

1. Precompile your collections manually at build-time
2. Build the data cascade for the project (no rendering required)

Precompile Collections at Build-Time Jump to heading #

In this example we’ll build a static data file with collections data in it at build time and inject it into our serverless build at run time!

Consider a sidebarNav collection that populates a navigation menu (via the eleventy-navigation plugin).

module.exports = function(eleventyConfig) {
	eleventyConfig.addCollection("sidebarNav", function(collection) {
		return collection.getAll().filter(item => item.data?.eleventyNavigation);
	});
};

This might be used in your templates (serverless or build) via {{ collections.sidebarNav | eleventyNavigation }}.

Now, the sidebarNav collection would not normally be available in a serverless context, because all of the templates that populate the menu are not in the scope of the serverless build. But we can generate a static copy of that collection for use in serverless mode. In fact, this is how the sidebar works on each (serverless) Author’s page (e.g. the one for @zachleat).

Consider the following Eleventy template which creates an array of collection-like entries for the sidebar navigation.

exports.data = function() {
  return {
    // generate directly to the serverless bundle folder
    permalink: "./netlify/functions/serverless/_generated-serverless-collections.json",
    permalinkBypassOutputDir: true,
		eleventyExcludeFromCollections: true,
  };
};

exports.render = function({collections}) {
  let entries = [];
  // Iterate over any items with the `sidebarNav` tag
  for(let entry of collections.sidebarNav) {
    entries.push({
      data: {
        page: entry.data.page,
        eleventyNavigation: entry.data.eleventyNavigation,
      }
    });
  }

  return JSON.stringify({
    sidebarNav: entries
  }, null, 2);
};

const precompiledCollections = require("./_generated-serverless-collections.json");

async function handler (event) {
	let elev = new EleventyServerless("possum", {
		path: event.path,
		query: event.queryStringParameters,
		precompiledCollections
	});

	// Some content truncated
};

Compile the data cascade for the project Jump to heading #

As we have just learned, Eleventy Serverless operates on a subset of templates in your project. You can disable this subset scope with the singleTemplateScope option on the EleventyServerless class (defaults to true). Added in v2.0.0

This uses incremental builds with the new ignore initial build feature to only render one file (while building the larger data cascade for the project). The downside here is that while this is much friendlier to any use of collections on your templates, it is slower! Here are the conditions I’d expect folks to want to make this tradeoff:

• If your project is small/fast enough and you don’t want to spend the extra development effort.
• If your project is larger but you’re using On-demand Builders where the extra rendering cost is only paid once.
• For larger projects I would not recommend use of singleTemplateScope: false in a dynamic template that renders with each request.

Here’s how to enable this feature in your serverless function file:

async function handler (event) {
	let elev = new EleventyServerless("possum", {
		path: event.path,
		query: event.queryStringParameters,
		singleTemplateScope: false, // true by default
	});

	// Some content truncated
};

At some point we may enable this feature by default if performance improves enough!

Swap to Dynamic using the Data Cascade and eleventyComputed Jump to heading #

In this example we’re using a global data entry to control whether a downstream temple renders in serverless or build mode (at build time). In some more limited use cases this can solved using your hosting providers Redirects feature (e.g. on Netlify this means a netlify.toml or _redirects file).

If you want to make a decision at serverless runtime to render a build template, you’ll need to add logic to your serverless function to redirect to the build URL from the serverless template.

module.exports = function(eleventyConfig) {
	// Templates will generate via the Build
	eleventyConfig.addGlobalData("runInServerlessMode", false);

	// Or render in Serverless mode
	eleventyConfig.addGlobalData("runInServerlessMode", true);
};

And then in your template files you can use this global data value with Computed Data to swap rendering modes:

---js
{
	eleventyComputed: {
		permalink: function({runInServerlessMode}) {
			return {
				[runInServerlessMode ? "serverless" : "build"]: "/"
			}
		}
	}
}
---
Template Content goes here

• If you’re here you may also be interested in the Eleventy Serverless OAuth demo

For internal use

Dependency Bundle Sizes

Bundle size	Package name
	@11ty/eleventy
	@11ty/eleventy@canary
	@11ty/eleventy-img
	@11ty/eleventy-fetch
	@11ty/eleventy-plugin-syntaxhighlight
	@11ty/eleventy-navigation
	@11ty/eleventy-plugin-vue
	@11ty/eleventy-plugin-rss

Other pages in Plugins:

• Edge
• Serverless
• Image
• Fetch
• Partial Hydration <is-land>
• Render
• Internationalization (i18n)
• RSS
• Syntax Highlighting
• Navigation
• HTML <base>
• Directory Output
• Inclusive Language