How to self-host your Next.js application

Source URL: https://nextjs.org/docs/app/guides/self-hosting

How to self-host your Next.js application

When deploying your Next.js app, you may want to configure how different features are handled based on your infrastructure.

🎥 Watch: Learn more about self-hosting Next.js → YouTube (45 minutes).

Reverse Proxy

When self-hosting, it’s recommended to use a reverse proxy (like nginx) in front of your Next.js server rather than exposing it directly to the internet. A reverse proxy can handle malformed requests, slow connection attacks, payload size limits, rate limiting, and other security concerns, offloading these tasks from the Next.js server. This allows the server to dedicate its resources to rendering rather than request validation.

Image Optimization

Image Optimization through next/image works self-hosted with zero configuration when deploying using next start. If you would prefer to have a separate service to optimize images, you can configure an image loader.

Image Optimization can be used with a static export by defining a custom image loader in next.config.js. Note that images are optimized at runtime, not during the build.

Good to know:

• On glibc-based Linux systems, Image Optimization may require additional configuration to prevent excessive memory usage.
• Learn more about the caching behavior of optimized images and how to configure the TTL.
• You can also disable Image Optimization and still retain other benefits of using next/image if you prefer. For example, if you are optimizing images yourself separately.

Proxy

Proxy works self-hosted with zero configuration when deploying using next start. Since it requires access to the incoming request, it is not supported when using a static export.

Proxy uses the Edge runtime, a subset of all available Node.js APIs to help ensure low latency, since it may run in front of every route or asset in your application. If you do not want this, you can use the full Node.js runtime to run Proxy.

If you are looking to add logic (or use an external package) that requires all Node.js APIs, you might be able to move this logic to a layout as a Server Component. For example, checking headers and redirecting. You can also use headers, cookies, or query parameters to redirect or rewrite through next.config.js. If that does not work, you can also use a custom server.

Environment Variables

Next.js can support both build time and runtime environment variables.

By default, environment variables are only available on the server. To expose an environment variable to the browser, it must be prefixed with NEXT_PUBLIC_. However, these public environment variables will be inlined into the JavaScript bundle during next build.

You safely read environment variables on the server during dynamic rendering.

import { connection } from 'next/server'

export default async function Component() {
  await connection()
  // cookies, headers, and other Dynamic APIs
  // will also opt into dynamic rendering, meaning
  // this env variable is evaluated at runtime
  const value = process.env.MY_VALUE
  // ...
}

import { connection } from 'next/server'

export default async function Component() {
  await connection()
  // cookies, headers, and other Dynamic APIs
  // will also opt into dynamic rendering, meaning
  // this env variable is evaluated at runtime
  const value = process.env.MY_VALUE
  // ...
}

This allows you to use a singular Docker image that can be promoted through multiple environments with different values.

Good to know:

• You can run code on server startup using the register function.

Caching and ISR

Next.js can cache responses, generated static pages, build outputs, and other static assets like images, fonts, and scripts.

Caching and revalidating pages (with Incremental Static Regeneration) use the same shared cache. By default, this cache is stored to the filesystem (on disk) on your Next.js server. This works automatically when self-hosting using both the Pages and App Router.

You can configure the Next.js cache location if you want to persist cached pages and data to durable storage, or share the cache across multiple containers or instances of your Next.js application.

Automatic Caching

• Next.js sets the Cache-Control header of public, max-age=31536000, immutable to truly immutable assets. It cannot be overridden. These immutable files contain a SHA-hash in the file name, so they can be safely cached indefinitely. For example, Static Image Imports. You can configure the TTL for images.
• Incremental Static Regeneration (ISR) sets the Cache-Control header of s-maxage: <revalidate in getStaticProps>, stale-while-revalidate. This revalidation time is defined in your getStaticProps function in seconds. If you set revalidate: false, it will default to a one-year cache duration.
• Dynamically rendered pages set a Cache-Control header of private, no-cache, no-store, max-age=0, must-revalidate to prevent user-specific data from being cached. This applies to both the App Router and Pages Router. This also includes Draft Mode.

Static Assets

If you want to host static assets on a different domain or CDN, you can use the assetPrefix configuration in next.config.js. Next.js will use this asset prefix when retrieving JavaScript or CSS files. Separating your assets to a different domain does come with the downside of extra time spent on DNS and TLS resolution.

Learn more about assetPrefix.

Configuring Caching

By default, generated cache assets will be stored in memory (defaults to 50mb) and on disk. If you are hosting Next.js using a container orchestration platform like Kubernetes, each pod will have a copy of the cache. To prevent stale data from being shown since the cache is not shared between pods by default, you can configure the Next.js cache to provide a cache handler and disable in-memory caching.

To configure the ISR/Data Cache location when self-hosting, you can configure a custom handler in your next.config.js file:

module.exports = {
  cacheHandler: require.resolve('./cache-handler.js'),
  cacheMaxMemorySize: 0, // disable default in-memory caching
}

Then, create cache-handler.js in the root of your project, for example:

const cache = new Map()

module.exports = class CacheHandler {
  constructor(options) {
    this.options = options
  }

  async get(key) {
    // This could be stored anywhere, like durable storage
    return cache.get(key)
  }

  async set(key, data, ctx) {
    // This could be stored anywhere, like durable storage
    cache.set(key, {
      value: data,
      lastModified: Date.now(),
      tags: ctx.tags,
    })
  }

  async revalidateTag(tags) {
    // tags is either a string or an array of strings
    tags = [tags].flat()
    // Iterate over all entries in the cache
    for (let [key, value] of cache) {
      // If the value's tags include the specified tag, delete this entry
      if (value.tags.some((tag) => tags.includes(tag))) {
        cache.delete(key)
      }
    }
  }

  // If you want to have temporary in memory cache for a single request that is reset
  // before the next request you can leverage this method
  resetRequestCache() {}
}

Using a custom cache handler will allow you to ensure consistency across all pods hosting your Next.js application. For instance, you can save the cached values anywhere, like Redis or AWS S3.

Good to know:

• revalidatePath is a convenience layer on top of cache tags. Calling revalidatePath will call the revalidateTag function with a special default tag for the provided page.

Build Cache

Next.js generates an ID during next build to identify which version of your application is being served. The same build should be used and boot up multiple containers.

If you are rebuilding for each stage of your environment, you will need to generate a consistent build ID to use between containers. Use the generateBuildId command in next.config.js:

module.exports = {
  generateBuildId: async () => {
    // This could be anything, using the latest git hash
    return process.env.GIT_HASH
  },
}

Multi-Server Deployments

When running Next.js across multiple server instances (for example, containers behind a load balancer), there are additional considerations to ensure consistent behavior.

Server Functions encryption key

Next.js encrypts Server Function closure variables before sending them to the client. By default, a unique encryption key is generated for each build.

When running multiple server instances, all instances must use the same encryption key. Otherwise, a Server Function encrypted by one instance cannot be decrypted by another, causing “Failed to find Server Action” errors.

Set a consistent encryption key using the NEXT_SERVER_ACTIONS_ENCRYPTION_KEY environment variable. The key must be a base64-encoded value with a valid AES key length (16, 24, or 32 bytes). Next.js generates 32-byte keys by default.

NEXT_SERVER_ACTIONS_ENCRYPTION_KEY=your-generated-key next build

The key is embedded in the build output and used automatically at runtime. Learn more in the Data Security guide.

Deployment identifier

Configure a deploymentId to enable version skew protection during rolling deployments. This ensures clients always receive assets from a consistent deployment version.

Shared cache

By default, Next.js uses an in-memory cache that is not shared across instances. For consistent caching behavior, use 'use cache: remote' with a custom cache handler that stores data in external storage.

Version Skew

When self-hosting across multiple instances or doing rolling deployments, version skew can cause:

• Missing assets: The client requests JavaScript or CSS files that no longer exist on the server
• Server Function mismatches: The client invokes a Server Function using an ID from a previous build that the server no longer recognizes
• Navigation failures: Prefetched page data from an old deployment is incompatible with the new server

Next.js uses the deploymentId to detect and handle version skew. When a deployment ID is configured:

• Static assets include a ?dpl=<deploymentId> query parameter
• Client-side navigation requests include an x-deployment-id header
• The server compares the client’s deployment ID with its own

If a mismatch is detected, Next.js triggers a hard navigation (full page reload) instead of a client-side navigation. This ensures the client fetches assets from a consistent deployment version.

module.exports = {
  deploymentId: process.env.DEPLOYMENT_VERSION,
}

Good to know: When the application is reloaded, there may be a loss of application state if it’s not designed to persist between page navigations. URL state or local storage would persist, but component state like useState would be lost.

Streaming and Suspense

The Next.js App Router supports streaming responses when self-hosting. If you are using nginx or a similar proxy, you will need to configure it to disable buffering to enable streaming.

For example, you can disable buffering in nginx by setting X-Accel-Buffering to no:

module.exports = {
  async headers() {
    return [
      {
        source: '/:path*{/}?',
        headers: [
          {
            key: 'X-Accel-Buffering',
            value: 'no',
          },
        ],
      },
    ]
  },
}

Cache Components

Cache Components works by default with Next.js and is not a CDN-only feature. This includes deployment as a Node.js server (through next start) and when used with a Docker container.

Usage with CDNs

When using a CDN in front of your Next.js application, the page will include Cache-Control: private response header when dynamic APIs are accessed. This ensures that the resulting HTML page is marked as non-cacheable. If the page is fully prerendered to static, it will include Cache-Control: public to allow the page to be cached on the CDN.

If you don’t need a mix of both static and dynamic components, you can make your entire route static and cache the output HTML on a CDN. This Automatic Static Optimization is the default behavior when running next build if dynamic APIs are not used.

As Partial Prerendering moves to stable, we will provide support through the Deployment Adapters API.

after

after is fully supported when self-hosting with next start.

When stopping the server, ensure a graceful shutdown by sending SIGINT or SIGTERM signals and waiting. This allows the Next.js server to wait until after pending callback functions or promises used inside after have finished.