In IIS 7, the default HTTP keep-alive timeout is set to 120 seconds (2 minutes). This means that by default, a connection will remain open for reuse for 2 minutes after completing a request, unless explicitly closed by either the client or server.

HTTP Keep-Alive is crucial for performance optimization in web applications. Maintaining persistent connections reduces:

• TCP connection overhead
• SSL/TLS handshake costs
• Latency for subsequent requests

You can modify this setting through several approaches:

1. Using ApplicationHost.config

<system.applicationHost>
    <webLimits connectionTimeout="00:02:00" />
</system.applicationHost>

2. Via IIS Manager

1. Open IIS Manager
2. Select the server node
3. Double-click "Configuration Editor"
4. Navigate to system.applicationHost/webLimits
5. Modify the connectionTimeout value

3. PowerShell Automation

Import-Module WebAdministration
Set-WebConfigurationProperty -pspath 'MACHINE/WEBROOT/APPHOST' 
-filter "system.applicationHost/webLimits" 
-name "connectionTimeout" 
-value "00:01:30"

Use this C# code to test your current keep-alive settings:

HttpWebRequest request = (HttpWebRequest)WebRequest.Create("http://yoursite.com");
request.KeepAlive = true;
using (HttpWebResponse response = (HttpWebResponse)request.GetResponse())
{
    Console.WriteLine("Connection header: " + response.Headers["Connection"]);
    Console.WriteLine("Keep-Alive timeout: " + response.Headers["Keep-Alive"]);
}

For load-balanced environments, consider using ARR (Application Request Routing) with these settings in applicationHost.config:

<webFarms>
    <webFarm name="Farm1" enabled="true">
        <server address="server1" enabled="true">
            <applicationRequestRouting httpPort="80" />
        </server>
        <applicationRequestRouting>
            <protocol timeout="00:02:00" />
        </applicationRequestRouting>
    </webFarm>
</webFarms>

Remember that the effective keep-alive behavior depends on both server configuration and client HTTP headers. Modern browsers typically have their own keep-alive strategies that interact with these server settings.

HTTP Keep-Alive is a critical performance feature that maintains TCP connections between client and server for multiple requests. In IIS7, the default keep-alive timeout is 120 seconds (2 minutes). This setting determines how long the server maintains an idle connection before closing it.

You can verify the current keep-alive timeout through IIS Manager or by examining the applicationHost.config file:

<system.applicationHost>
    <httpProtocol>
        <headerLimits>
            <add name="Keep-Alive" value="120" />
        </headerLimits>
    </httpProtocol>
</system.applicationHost>

To adjust this value programmatically using C#:

using Microsoft.Web.Administration;

ServerManager serverManager = new ServerManager();
Configuration config = serverManager.GetApplicationHostConfiguration();
ConfigurationSection httpProtocolSection = config.GetSection("system.webServer/httpProtocol");
ConfigurationElementCollection headerLimitsCollection = httpProtocolSection.GetCollection("headerLimits");

ConfigurationElement addElement = headerLimitsCollection.CreateElement("add");
addElement["name"] = "Keep-Alive";
addElement["value"] = "60"; // New timeout in seconds
headerLimitsCollection.Add(addElement);

serverManager.CommitChanges();

Factors to consider when adjusting keep-alive timeout:

• Higher values reduce TCP handshake overhead but may consume server resources
• Lower values free up connections faster but increase connection establishment latency
• For high-traffic sites, typically set between 30-120 seconds

Example configuration for various use cases:

// API server with frequent requests from same clients
ConfigurationElement apiSetting = headerLimitsCollection.CreateElement("add");
apiSetting["name"] = "Keep-Alive";
apiSetting["value"] = "300"; // 5 minutes

// Static content server with infrequent requests
ConfigurationElement staticSetting = headerLimitsCollection.CreateElement("add");
staticSetting["name"] = "Keep-Alive";
staticSetting["value"] = "30"; // 30 seconds