Origin Rules settings

import { Example } from "~/components";

The following sections describe the available settings in Origin Rules.

Host header

Allows you to rewrite the HTTP Host header of incoming requests. The Host header tells the destination server which website or application the request is intended for.

A common use case for this functionality is when your content is hosted on a third-party server that only accepts Host headers with their own server names. In this situation, you must update the Host HTTP header in incoming requests from Host: example.com to Host: thirdpartyserver.example.net.

:::note[Notes]

• In most situations, when you rewrite the HTTP Host header you also need to configure a DNS record override. The Host header override only updates the header value; the DNS record override will handle the rerouting of the request.

• An origin rule performing a Host header override will also update the Server Name Indication (SNI) value of the original request to the same value. To set an SNI value different from the Host header value, add an SNI override in the same origin rule or create a separate origin rule for this purpose.

• If you have configured load balancing through Cloudflare and you wish to override the HTTP Host header per origin or for a given monitor, refer to Override HTTP Host headers in the Load Balancing documentation for more information.

• When an origin rule is configured to override the Host header for a request handled by a Worker, this override is not taken into account when evaluating Workers routes.

:::

Server Name Indication (SNI)

Allows you to override the Server Name Indication (SNI) [^1] value of a request. For more information, refer to What is SNI (Server Name Indication)? in the Learning Center.

:::note[Notes]

• The new SNI value must be a valid hostname on the same Cloudflare account (possibly on a different zone).
• Currently, you can only use a static value when overriding SNI.
• An SNI override will take precedence over SNI rewrites of custom origins when using Cloudflare for SaaS.

:::

[^1]: SNI allows a server to host multiple TLS Certificates for multiple websites using a single IP address. SNI adds the website hostname in the TLS handshake to inform the server which website to present when using shared IPs.

DNS record

Allows you to override the resolved hostname of incoming requests, which controls which origin server Cloudflare sends the request to. This functionality is also known as resolve override.

A common use case is when you are serving an application from a specific path (for example, mydomain.com/app). In this case, the app may be hosted on a different server or by a third party. A DNS record override allows you to redirect requests to this endpoint to the server for that third-party application.

:::note

• You must specify a valid hostname in a DNS record override that is a hostname on the same Cloudflare account (possibly on a different zone). You can configure a DNS record (a CNAME, A, or AAAA record) with a hostname pointing to a third-party hostname/IP address, either proxied by Cloudflare or not.

• In most situations, when you configure a DNS record override you also need to configure a Host header override. The DNS record override handles the rerouting of the request; the Host header override updates the Host HTTP header value in the request. Defining a Host header override will also update the Server Name Indication (SNI) value of the original request to the same value. To set an SNI value different from the Host header value, add an SNI override in the same origin rule or create a separate origin rule for this purpose.

:::

The following example DNS records configure a resolve.example.com hostname pointing to an external hostname and IP address using a CNAME record and an A record, respectively:

Example CNAME record

• Type: CNAME
• Name: resolve.example.com
• Target: domain.s3.amazonaws.com
• TTL: Auto
• Proxy status: Proxied (orange cloud icon)

Example A record

• Type: A
• Name: resolve.example.com
• IPv4 address: 203.0.113.1
• TTL: Auto
• Proxy status: Proxied (orange cloud icon)

Destination port

Allows you to override the destination port of a request.

When you configure a destination port override, you can redirect incoming requests to a different port. For example, you could override the destination port for requests received for mydomain.com so that they are served by the application running on port 9000 (mydomain.com:9000).

The destination port must be between 1 and 65,535.