HTTP Headers
Keep Alive
HTTP Header
The HTTP Keep-Alive request and response headers enable the sender to suggest how a connection should be maintained, including specifying a timeout period and a maximum number of requests.
HTTP/1.0 closes the connection after each request-response cycle by default, requiring explicit negotiation for persistent connections.
Some clients and servers aim for compatibility with earlier persistent connection methods by including the Connection: keep-alive header in requests.
Additional parameters for the connection, such as timeout and maximum requests, can be requested using the Keep-Alive header.
Syntax
Keep-Alive: <parameters>Directives
A comma-separated list of parameters, each consisting of an identifier and a value separated by the equal sign (
The following identifiers are possible:
=).The following identifiers are possible:
- timeout
- An integer that specifies the duration in seconds before the host closes an idle connection. A connection is considered idle if no data is sent or received. While a host can keep an idle connection open longer than this timeout, it should aim to retain the connection for at least this duration.
- max
- An integer indicating the maximum number of requests allowed on this connection before it is closed. Unless set to
0, this limit is ignored for non-pipelined connections, where another request can be sent in the next response. This setting can be used to control pipelining in HTTP.
Example
A response containing a Keep-Alive header:
http
HTTP/1.1 200 OK
Connection: Keep-Alive
Content-Encoding: gzip
Content-Type: text/html; charset=utf-8
Date: Thu, 11 Aug 2016 15:23:13 GMT
Keep-Alive: timeout=5, max=200
Last-Modified: Mon, 25 Jul 2016 04:32:39 GMT
Server: Apache
(body)
How to Modify Header using Requestly
Requestly is a powerful Chrome extension that allows you to modify HTTP headers, including the Keep-Alive header. This is especially useful for testing how your application handles persistent connections and to troubleshoot connection management issues. Steps to Modify the Keep-Alive Header:
- Install and open the Requestly Chrome extension. You can find it on the Chrome Web Store.
- Create a new rule: Click on “Create Rule” and choose “Modify Headers” from the list of available rule types.
- Add a new header modification:
- Under “Action”, select “Add” or “Override”.
- In the “Header Name” field, enter Keep-Alive.
- In the “Header Value” field, enter your desired configuration (e.g., timeout=5, max=100).
- Set the URL condition: Specify the URL or pattern where this header change should apply (e.g., https://your-api.com/*).
- Save the rule.
Once set up, Requestly will inject the Keep-Alive header with your specified values into all matching requests, enabling you to test and optimize how your application manages persistent HTTP connections.
Modifying the Keep-Alive header is helpful because it controls how long a connection stays open between client and server. This can improve performance by reducing connection overhead or help debug connection timeout issues.
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