What is the difference between On Request and On Response actions?

Short answer

On Request actions are applied to the request before it goes to the Backend Service (such as adding a request header, redirecting, blocking). On Response actions are applied to the response returned from the Backend Service, before it is forwarded to the client (such as adding a response header, changing the response content). In action types that can run in both phases, the phase is selected in the Execution Level field; the default is On Request, and it cannot be changed after the action is saved. The phase of the other types is fixed.

How Does It Work?

1. The client's request reaches TR7; the On Request actions on the vService are applied to the request in order.
2. The request is forwarded to the Backend Service and the response returns.
3. The On Response actions are applied to the response in order, and the response is sent to the client.

Comparison

	On Request	On Response
When	Before the request goes to the Backend Service	Before the response returns to the client
What it is applied to	The request	The response of the Backend Service
Selectable conditions	Request-stage conditions (Path, HTTP Header, Source IP…)	Response-stage conditions as well (Status Code, Server Response Time, Response Size (bytes)…)
Typical use	Blocking, redirection, request header, path change	Security headers, response header, response content

Execution Level in TR7

• The Execution Level field appears only in the types that can run in both phases: Show Content, Add HTTP Header, Delete HTTP Header, Set HTTP Header, Replace HTTP Header Content, Create Traffic Variable, Advanced Traffic Inspection, Conditional Silent Log, Manual Action, Block, TCP Connection Management and Quarantine (action types).
• The phase of the other types is fixed. For example, Location Redirection, Set Path and Redirect to HTTPS are only in the request stage; Manage HTTP Security Headers, HTTP Cookie Security and Modify Response Content are only in the response stage.
• When the phase is changed in a new action, the selected conditions are reset; the condition list is filtered according to the selected phase.
• In Conditional Backend Services blocks, since the Backend Service selection is made in the request stage, only request-stage conditions can be selected.

Common Misconceptions

• "On Request is enough to add a response header." To add a header to the response, On Response must be selected; On Request adds the header to the request going to the Backend Service.
• "An On Response action is also applied to the responses that TR7 produces." Most On Response actions are not applied to the responses that TR7 produces itself with Block, Show content or redirection; HTTP Cookie Security is the exception to this (If an action blocks or redirects traffic, do the subsequent actions run?).
• "The phase can be changed later." After saving, Execution Level and Action type are locked; a new action is created for a different phase.
• "Tarpit can be selected in every phase." In the Block action, Tarpit can be selected only in On Request; when the phase is set to On Response, the Tarpit selection is removed.

How it is done in the documentation

• Actions · On Request
• Actions · On Response
• Add HTTP Header · Execution Level
• Block · Deny Type

Related questions

• If an action blocks or redirects traffic, do the subsequent actions run?
• Can I make decisions based on backend response time or response status code?
• In what order do Actions run; how do I change the order?