---
title: "Configure content caching"
sidebar_label: "Configure caching"
description: "How to configure caching time, how to serve content on source errors, and other instructions"
sidebar_position: 2
---

import Formbricks from '@theme/MDXComponents/Formbricks'
import PlusIcon from 'docs-kit/icons/plus'

# Configure content caching

By default, content caching settings are disabled. You can enable and configure them:

* [caching time](#set-caching-time);
* [serving content from cache on source errors](#return-content-from-cache-on-source-errors);
* [caching content by query string](#cache-content-with-query-string);
* [caching content by cookies](#cache-content-with-cookies).

## Configure caching time \{#set-caching-time}

The caching time is the duration for which CDN servers store a copy of the response from the origin before re-requesting content. Caching time can be configured for each HTTP response.

1. In the [control panel](https://my.selectel.ru/cdn-v3), on the top menu, click **Products** and select **CDN**.

2. In the **CDN Resources** section, open the CDN resource page → **Caching** tab.

3. Check the **Enable caching settings** checkbox.

4. In the **Content caching time** block, configure the caching time for each response type:

   * for `2xx` — retention time for successful responses;
   * `3xx` — retention time for redirects;
   * `4xx` — retention time for client errors;
   * `5xx` — retention time for server errors;
   * in browser — the time the browser can cache a response after receiving it from the CDN.

5. To override the content source settings with your own, check the **Ignore cache control headers** checkbox. The CDN will ignore `Cache-Control` and `Expires` headers that contain caching information from the content source.

6. Click **Apply**. While settings are being applied, the CDN resource enters the `PROCESSING` status. You cannot apply other settings during this time. Settings take effect when the CDN resource transitions to `ACTIVE`.

## Serve content from cache on source errors \{#return-content-from-cache-on-source-errors}

If the content source returns an error, the user can receive the last cached version of the content (Use Stale). While the source is unavailable, site pages may not display correctly: for example, some images, videos, or stylesheets may not work. CDN servers will check the availability of the source with each new request:

* if the error persists, CDN servers will serve the last cached content with the `Cache: Stale` header;
* if the source functionality is restored, the CDN server will cache the fresh version of the file.

To serve content from cache on source errors:

1. In the [control panel](https://my.selectel.ru/cdn-v3), on the top menu, click **Products** and select **CDN**.

2. In the **CDN Resources** section, open the CDN resource page → **Caching**.

3. Check the **Enable caching settings** checkbox.

4. In the **Last cached content version (Use Stale)** block, check the **Serve the last cached version if the source is unavailable**.

5. In the **Serve stale content on** list, select the errors that should trigger serving the last cached content:

   * `error` — connection error to the server;
   * `timeout` — connection timeout with the server;
   * `invalid_header` — the server returned an empty or invalid response;
   * `updating` — serve stale cached response while files in cache are being updated;
   * `http_500` — internal server error;
   * `http_502` — bad gateway error;
   * `http_503` — server cannot process the request;
   * `http_504` — gateway timeout;
   * `http_403` — forbidden error;
   * `http_404` — CDN resource not found;
   * `http_429` — too many requests.

6. Click **Apply**. While settings are being applied, the CDN resource enters the `PROCESSING` status. You cannot apply other settings during this time. Settings take effect when the CDN resource transitions to `ACTIVE`.

## Cache content by query string \{#cache-content-with-query-string}

By default, the CDN ignores query strings (query string).

You can enable caching content by query string.

If requests to the same file contain different parameters (the part after the question mark in the file URL), each request with a new parameter is redirected to the source.

1. In the [control panel](https://my.selectel.ru/cdn-v3), on the top menu, click **Products** and select **CDN**.

2. In the **CDN Resources** section, open the CDN resource page → **Caching**.

3. Check the **Enable caching settings** checkbox.

4. In the **Cache by query string** block, check the **Cache by query string** checkbox. By default, all query parameters will be considered.

5. If you want to consider specific request parameters, uncheck the **Consider all parameters** checkbox.

6. Enter the query parameter. You can enter an allowed or forbidden parameter:

   * to specify an allowed parameter, enable **White List**, add the parameter, and click <PlusIcon />. Only parameters included in this list will be considered when processing requests.

   * to specify a forbidden parameter, enable **Black List**, add the parameter, and click <PlusIcon />. All parameters not included in this list will be considered when processing requests.

7. To add another query parameter, repeat step 6.

8. Click **Apply**. While settings are being applied, the CDN resource enters the `PROCESSING` status. You cannot apply other settings during this time. Settings take effect when the CDN resource transitions to `ACTIVE`.

## Cache content by cookies \{#cache-content-with-cookies}

By default, the CDN ignores cookies.

You can enable content caching based on cookie parameters.

The CDN caches one file with different cookies from the HTTP request header as distinct files, and every new user request is forwarded to the origin.

1. In the [control panel](https://my.selectel.ru/cdn-v3), click **Products** on the top menu and select **CDN**.

2. In the **CDN Resources** section, open the CDN resource page → **Caching**.

3. Select the **Enable caching settings** checkbox.

4. In the **Cache by cookies** section, select the **Cache by cookies** checkbox. By default, all cookies will be considered.

5. If you want to consider specific cookies in the request, clear the **Consider all parameters** checkbox.

6. Enter the cookie parameter. You can enter an allowed or forbidden parameter:

   * to enter an allowed cookie parameter, enable **White List**, add the allowed parameter, and click <PlusIcon />. Only cookie parameters included in this list will be considered when processing requests;

   * to enter a forbidden cookie parameter, enable **Black List**, add the forbidden parameter, and click <PlusIcon />. All parameters that are not included in this list will be considered when processing requests.

7. To add another cookie parameter, repeat step 6.

8. Click **Apply**. While settings are being applied, the CDN resource enters the `PROCESSING` status. You cannot apply other settings during this time. Settings take effect when the CDN resource transitions to `ACTIVE`.

<Formbricks />