Change the HTTP Host header

The following origin rule overrides the HTTP Host header to eu_server.example.net for all requests containing /eu/ in their URI path.

Dashboard

Text in Expression Editor:

http.request.uri.path contains "/eu/"

Value after Host Header > Rewrite to:

eu_server.example.net

API

The following example sets the rules of an existing phase ruleset ($RULESET_ID) to a single origin rule — overriding the HTTP Host header — 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": [
        {
            "expression": "http.request.uri.path contains \"/eu/\"",
            "description": "My first origin rule",
            "action": "route",
            "action_parameters": {
                "host_header": "eu_server.example.net"
            }
        }
    ]
  }'

{
  "result": {
    "id": "<RULESET_ID>",
    "name": "Origin Rules ruleset",
    "description": "Zone-level ruleset that will execute origin rules.",
    "kind": "zone",
    "version": "2",
    "rules": [
      {
        "id": "<RULE_ID>",
        "version": "1",
        "action": "route",
        "action_parameters": {
          "host_header": "eu_server.example.net"
        },
        "expression": "http.request.uri.path contains \"/eu/\"",
        "description": "My first origin rule",
        "last_updated": "2022-06-02T14:42:04.219025Z",
        "ref": "<RULE_REF>"
      }
    ],
    "last_updated": "2022-06-02T14:42:04.219025Z",
    "phase": "http_request_origin"
  },
  "success": true,
  "errors": [],
  "messages": []
}