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Header Manipulation

The Envoy HTTP connection manager allows HTTP header manipulations both when the request is being received and when the response is being sent. The official documentation can be found here. Grey Matter utilizes this to manipulate HTTP headers at several levels and also allows users to add their own custom headers.

The order of header precedence is:

  1. Weighted cluster level headers
  2. Route level headers
  3. Virtual host level headers
  4. Global level headers

Header manipulations

In order to keep track of potential overwrites of header values, we will go over places we can add custom headers in the order of precedence. Envoy supports some variables mentioned here.

2. Virtual host level headers

You can append your custom headers by defining custom_headers at the Domain level:

{
  ...,
  "custom_headers": [
    {
      "key": "My-Custom-Header",
      "value": "hello-world"
    }
  ]
}

ℹ️ The custom headers specified here will be added to Envoy virtual host's request.

4. Weighted cluster level headers

  • 4.1 Edge Route response_data
  • 4.2 Service Route response_data
  • 4.3 Edge SharedRules response_data
  • 4.4 ServiceSharedRules response_data

Routes and SharedRules both have response_data, and values from a Route take precedence over those from a SharedRules object. Between Edge's Route/SharedRules and a service's (e.g. Fibonacci service), Edge's headers take precedence; while cookies get appended.

Cookies are attached via Set-Cookie header and we can use aforementioned Envoy variables by setting value_is_literal to false. On the other hand, by setting value_is_literal to true, the % literal can be used without escaping.

{
  ...,
  "response_data": {
    "headers": [
      {
        "name": "My-Custom-Header",
        "value": "hello-world",
        "value_is_literal": true
      }
    ],
    "cookies": [
      {
        "name": "my_cookie",
        "value": "cookie-value",
        "value_is_literal": true,
        "expires_in_sec": 60000,
        "domain": "a5c047016227111ea9bff0295a6daf52-1281033796.us-west-2.elb.amazonaws.com",
        "path": "/",
        "secure": true,
        "http_only": true,
        "same_site": "Lax"
      }
    ]
  }
}

As the name suggests, headers specified here will be added to Envoy weighted cluster's response.

Here are naming pattern for Header and Cookie:

HeaderNamePatternStr = "^[0-9A-Za-z-]+$"
CookieNamePatternStr = "^[0-9A-Za-z_.-]+$"