Change the HTTP Host header and DNS record

The following origin rule overrides the HTTP Host header to hr-server.example.com for all requests with a URI path starting with /hr-app/. It also overrides the DNS record to the same hostname.

The Host header override only updates the header value; the DNS record override will handle the rerouting of incoming requests. For more information on these overrides, refer to Available settings.

Dashboard

Expression when using the Expression Builder:

Field	Operator	Value
URI Path	starts with	/hr-app/

Expression when using the Expression Editor:

(starts_with(http.request.uri.path, "/hr-app/"))

Value after Host Header > Rewrite to:

hr-server.example.com

Value after DNS Record > Override to:

hr-server.example.com

API

The following example sets the rules of an existing phase ruleset ($RULESET_ID) to a single origin rule — overriding the Host header of incoming requests and the resolved DNS record — using the Update a zone ruleset operation. The response will contain the complete definition of the ruleset you updated.

Required API token permissions

At least one of the following token permissions is required:

• Response Compression Write
• Config Settings Write
• Dynamic URL Redirects Write
• Cache Settings Write
• Custom Errors Write
• Origin Write
• Managed headers Write
• Zone Transform Rules Write
• Mass URL Redirects Write
• Magic Firewall Write
• L4 DDoS Managed Ruleset Write
• HTTP DDoS Managed Ruleset Write
• Sanitize Write
• Transform Rules Write
• Select Configuration Write
• Bot Management Write
• Zone WAF Write
• Account WAF Write
• Account Rulesets Write
• Logs Write
• Logs Write

Update a zone ruleset

curl "https://api.cloudflare.com/client/v4/zones/$ZONE_ID/rulesets/$RULESET_ID" \
  --request PUT \
  --header "Authorization: Bearer $CLOUDFLARE_API_TOKEN" \
  --json '{
    "rules": [
        {
            "ref": "hr_app_overrides",
            "expression": "starts_with(http.request.uri.path, \"/hr-app/\")",
            "description": "Origin rule for the company HR application",
            "action": "route",
            "action_parameters": {
                "host_header": "hr-server.example.com",
                "origin": {
                    "host": "hr-server.example.com"
                }
            }
        }
    ]
  }'

{
  "result": {
    "id": "<RULESET_ID>",
    "name": "Origin Rules ruleset",
    "description": "Zone-level ruleset that will execute origin rules.",
    "kind": "zone",
    "version": "2",
    "rules": [
      {
        "ref": "hr_app_overrides",
        "id": "<RULE_ID>",
        "version": "1",
        "action": "route",
        "action_parameters": {
          "host_header": "hr-server.example.com",
          "origin": {
            "host": "hr-server.example.com"
          }
        },
        "expression": "starts_with(http.request.uri.path, \"/hr-app/\")",
        "description": "Origin rule for the company HR application",
        "last_updated": "2022-06-03T14:42:04.219025Z",
        "ref": "<RULE_REF>"
      }
    ],
    "last_updated": "2022-06-03T14:42:04.219025Z",
    "phase": "http_request_origin"
  },
  "success": true,
  "errors": [],
  "messages": []
}

Use the ref field to get stable rule IDs across updates when using Terraform. Adding this field prevents Terraform from recreating the rule on changes. For more information, refer to Troubleshooting in the Terraform documentation.