✅ IIS-Only Performance Optimization Settings (Complete List)

1. Application Pool Settings (IIS Core)

✔ Start Mode

• AlwaysRunning
  → Avoid cold starts.

✔ Idle Time-out

• Increase or disable (0) if you want warm apps.
  Default (20 min) causes unexpected pool shutdown.

✔ Worker Process Settings

• Maximum Worker Processes
  • Keep 1 (no web garden) for ASP.NET/Core.
  • Web gardens only for stateless apps.
• Queue Length
  • Increase from default 1000 to 5000–20000 depending on load.
    Prevents 503 (Queue full) errors.

✔ Recycling Settings

• Disable Regular Time-Based Recycling
  Stops unnecessary restarts.
• Enable Overlapped Recycling
  Zero-downtime recycling.
• Disable application pool recycling at idle
  (set Idle Time-out to 0).

2. Site-Level Performance Settings

✔ Connection Limits

• connectionTimeout
• maxConnections
• Keep-alive enabled.

✔ HTTP/2 & HTTP/3

• Enable HTTP/2 (and HTTP/3 on Windows Server 2022+) for higher throughput.

✔ Compression

(IIS → Compression feature)

• Enable Static Compression
• Enable Dynamic Compression
• Ensure compression for:
  • text/html
  • text/css
  • application/javascript
  • application/json

✔ Caching (Output Caching / Kernel Caching)

(IIS → Output Caching)

• Enable Kernel Caching (huge perf win for static files)
• Enable Output Caching for dynamic pages (if safe)
• Configure:
  • Cache duration
  • Vary-by rules

3. Static File Handling Settings

✔ Static Content

• Enable staticContent module
• Set cache-control headers (long max-age)
• Enable ETags or Last-Modified
• Make sure static file module is above ASP.NET modules.

4. IIS Modules Management (Pipeline)

✔ Disable/Remove Unused Modules

Huge performance improvement because every module executes per request.

Disable modules like:

• WebDAV
• ASP
• PHP (if not used)
• CGI
• ISAPI Filters
• Session State
• Windows Authentication (if not needed)
• Request Filtering (if handled by reverse proxy)

Goal: Lightest possible request pipeline.

5. Request Filtering (Limits)

✔ Max Request Size

• Tune maxAllowedContentLength
• Tune maxRequestLength

✔ URL Length Limits

• Prevent long-URL attacks.

✔ Header Limits

• Tune header size limits.

All these reduce bad requests hitting Kestrel or app layer.

6. Logging Settings

✔ W3C Logging

• Disable unnecessary fields
• Keep logs on separate fast disk
• Avoid logging ALL headers (expensive)

✔ Failed Request Tracing (FREB)

• Only enable for targeted diagnostics
• Turn off afterward

7. Application Initialization (Warm-Up)

(IIS → Configuration Editor → system.webServer/applicationInitialization)

• DoAppInitAfterRestart = True
• PreloadEnabled = True

This ensures app is warm and ready before first user hit.

8. Dynamic IP Restrictions (DoS protection)

Not directly performance but prevents IIS from being overwhelmed.

• Enable Dynamic Deny based on:
  • Request rate
  • Concurrent requests
  • Bad requests

9. WebSockets / Long-Running Connections Settings

• Enable only if needed.
• Disable WebSockets for performance if app does not use them.

10. Client Keep-Alive Settings

• Keep-alive enabled
• Keep-alive timeout tuned (15–120 seconds depending on use)

11. Centralized Configuration That Impacts Performance

✔ applicationHost.config

Key performance elements:

• <system.webServer/serverRuntime uploadReadAheadSize="…">
• <system.webServer/security/requestFiltering>
• <system.webServer/httpCompression>
• <system.webServer/webSocket>
• <system.webServer/cache>

12. Kernel-Mode Optimizations (HTTP.sys)

(These are still considered IIS-level because IIS sits on top of HTTP.sys)

✔ Enable Kernel Caching

→ Boosts static file performance massively.

✔ Set MaxBandwidth & MinFileBytesPrSec

→ Prevents slow clients from consuming server I/O.

✔ Enable URL ACL Tuning

→ Helps reduce request overhead.

🎯 FINAL OUTPUT

Exact list of IIS settings that impact performance:

App Pool

• AlwaysRunning
• Idle Timeout
• Recycling settings
• Maximum Worker Processes
• Queue Length

Compression

• Static compression
• Dynamic compression

Caching

• Kernel caching
• Output caching
• Static file caching

Modules

• Disable unused modules
• Optimize pipeline

Request filtering

• maxRequestLength
• maxAllowedContentLength
• URL/header limits

Connection settings

• connectionTimeout
• maxConnections
• Keep-alive

HTTP/2 / HTTP/3

• Enable

Logging

• Trim fields
• Optimize log location

Application Initialization

• PreloadEnabled
• DoAppInitAfterRestart

Static file handling

• cache-control headers
• ETags
• Last-Modified

Dynamic IP Restrictions

• Enable rate limiting

HTTP.sys kernel settings

• uploadReadAheadSize
• MinFileBytesPerSec
• MaxBandwidth

Here is the exact location of every IIS performance optimization setting — which GUI blade, which config file, or which PowerShell command you must use.

✅ 1. Application Pool Settings (All performance-critical)

1.1 Start Mode → “AlwaysRunning”

Where to configure:

• IIS Manager → Application Pools
• Select your App Pool → Advanced Settings
• Start Mode = AlwaysRunning

Config file:

applicationHost.config

<applicationPoolDefaults ... startMode="AlwaysRunning" />
Code language: HTML, XML (xml)

1.2 Idle Timeout

Where:

• IIS Manager → Application Pools → Your Pool → Advanced Settings
• Idle Time-out (minutes) → Set to 0 for performance-sensitive apps

Config:

<processModel idleTimeout="00:00:00"/>
Code language: HTML, XML (xml)

1.3 Recycling Settings

Where:

IIS Manager → Application Pools → Your Pool → Recycling…

Disable:

• Regular Time Interval
• Specific Time
• Memory-based recycling unless required

Config:

<recycling periodicRestart>
    <schedule />
</recycling>
Code language: HTML, XML (xml)

1.4 Queue Length

Where:

IIS Manager → Application Pools → Your Pool → Advanced Settings

• Queue Length = 5000–20000

Config:

<applicationPoolDefaults queueLength="20000" />
Code language: HTML, XML (xml)

1.5 Maximum Worker Processes

Where:

IIS Manager → Application Pools → Your Pool → Advanced Settings

• Maximum Worker Processes = 1 (no web garden)

Config:

<processModel maxProcesses="1" />
Code language: HTML, XML (xml)

✅ 2. Site-Level Settings

2.1 connectionTimeout + Keep-Alive

Where:

IIS Manager → Sites → Select Site → Limits…

You can configure:

• Connection timeout
• Max connections

Config:

<limits connectionTimeout="00:02:00" maxConnections="100000" />
Code language: HTML, XML (xml)

2.2 Enable HTTP/2 / HTTP/3

Where:

• Windows Features → HTTP/2 is enabled automatically if:
  • Server 2016+: HTTP/2 TLS
  • Server 2022+: HTTP/3 optional feature

Config:

<system.webServer>
  <httpProtocol allowKeepAlive="true" />
</system.webServer>
Code language: HTML, XML (xml)

✅ 3. Compression

3.1 Static Compression

3.2 Dynamic Compression

Where:

IIS Manager → Server or Site → Compression

• Enable:
  ✔ Static compression
  ✔ Dynamic compression

Config:

<urlCompression doStaticCompression="true" doDynamicCompression="true" />
Code language: HTML, XML (xml)

✅ 4. Caching

4.1 Output Caching

Where:

IIS Manager → Site → Output Caching

• Enable Cache
• Add caching rules

Config:

<caching enabled="true">
    <profiles>
        <add extension=".aspx" policy="CacheUntilChange" duration="3600"/>
    </profiles>
</caching>
Code language: HTML, XML (xml)

4.2 Kernel Caching

Where:

IIS Manager → Server → Feature Delegation
Ensure:

• Output Caching = Read/Write

Config:

<caching enableKernelCache="true" />
Code language: HTML, XML (xml)

✅ 5. Static File Handling

5.1 Cache-Control headers

Where:

IIS Manager → Site → HTTP Response Headers

• Add → Cache-Control: public, max-age=31536000

Config:

<httpProtocol>
    <customHeaders>
        <add name="Cache-Control" value="public, max-age=31536000" />
    </customHeaders>
</httpProtocol>
Code language: HTML, XML (xml)

✅ 6. Modules Optimization (DISABLING unused modules)

Where:

IIS Manager → Site → Modules

• Remove:
  • WebDAV
  • ASP
  • ISAPI Filters
  • CGI
  • Windows Authentication (if unused)

Config:

<modules>
   <remove name="WebDAV" />
   <remove name="ISAPI-filter" />
</modules>
Code language: HTML, XML (xml)

✅ 7. Request Filtering

7.1 Max Request Body Size

Where:

IIS Manager → Site → Request Filtering → Rules → Request Limits

• maxAllowedContentLength
• maxUrl
• maxQueryString

Config:

<requestFiltering>
  <requestLimits maxAllowedContentLength="52428800" />
</requestFiltering>
Code language: HTML, XML (xml)

✅ 8. Logging Settings

Where:

IIS Manager → Site → Logging

• Choose fields
• Directory location
• Format

Config:

<logFile enabled="true" directory="D:\IISLogs" logExtFileFlags="Date,Time,ClientIP,..." />
Code language: HTML, XML (xml)

✅ 9. Application Initialization (Warm-Up)

Where:

IIS Manager → Site → Configuration Editor
Section:
system.webServer/applicationInitialization

Set:

• doAppInitAfterRestart = true
• remapManagedRequestsTo = “true”
• preloadEnabled = true (in site → Advanced Settings)

Config:

<applicationInitialization doAppInitAfterRestart="true">
    <add initializationPage="/"/>
</applicationInitialization>
Code language: HTML, XML (xml)

✅ 10. Dynamic IP Restrictions

Where:

IIS Manager → Site → IP Address and Domain Restrictions

• Enable:
  • Deny By Concurrent Requests
  • Deny By Request Rate

Config:

<dynamicIpSecurity enableRateLimiting="true" maxRequests="200" requestIntervalInMilliseconds="500" />
Code language: HTML, XML (xml)

✅ 11. WebSocket Settings

Where:

IIS Manager → Site → WebSocket Protocol

• Disable if unused

Config:

<webSocket enabled="false" />
Code language: HTML, XML (xml)

✅ 12. HTTP.sys Kernel Settings

Where:

Registry or appcmd, but can be done via Configuration Editor under:
system.webServer/serverRuntime

uploadReadAheadSize

<serverRuntime uploadReadAheadSize="49152" />
Code language: HTML, XML (xml)

MinFileBytesPerSec

<serverRuntime minFileBytesPerSec="240" />
Code language: HTML, XML (xml)

🎯 FINAL SUMMARY (Mapped)

Rajesh Kumar

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