Tomcat HTTP Connector Configuration

The Tomcat HTTP Connector is the network entry point that receives client requests. Properly tuning parameters like maxThreads, acceptCount, and connectionTimeout can dramatically improve throughput and responsiveness.

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Basic Connector Structure

<!-- server.xml -->
<Connector port="8080"
           protocol="HTTP/1.1"
           connectionTimeout="20000"
           redirectPort="8443"/>

The protocol attribute determines which connector implementation is used.

Protocol Value	Implementation	Characteristics
HTTP/1.1	NIO (auto-selected)	Default, non-blocking I/O
org.apache.coyote.http11.Http11NioProtocol	NIO	Explicit NIO
org.apache.coyote.http11.Http11Nio2Protocol	NIO2	Async I/O
org.apache.coyote.http11.Http11AprProtocol	APR/Native	Requires native library

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Key Parameters

Thread Pool Configuration

<Connector port="8080" protocol="HTTP/1.1"
           maxThreads="200"
           minSpareThreads="10"
           maxSpareThreads="75"
           acceptCount="100"
           connectionTimeout="20000"/>

Parameter	Description	Default	Recommended
maxThreads	Max concurrent processing threads	200	CPU cores × 50~100
minSpareThreads	Minimum idle threads to maintain	10	10~25
maxSpareThreads	Maximum idle threads	75	maxThreads × 0.3
acceptCount	Queue size when all threads are busy	100	maxThreads × 0.5

Request flow:

Request arrives
    ↓
[Thread available?]
    ↓ Yes → Process immediately
    ↓ No  → Queue in acceptCount
              ↓ Queue full → Connection Refused

Timeout Configuration

<Connector port="8080" protocol="HTTP/1.1"
           connectionTimeout="20000"
           keepAliveTimeout="15000"
           maxKeepAliveRequests="100"/>

Parameter	Description	Default
connectionTimeout	Wait time for first request line (ms)	20000 (20s)
keepAliveTimeout	Keep-Alive connection duration (ms)	Value of connectionTimeout
maxKeepAliveRequests	Max requests per Keep-Alive connection	100

Production tip: If Nginx/Apache is in front, set keepAliveTimeout long enough to sync with the proxy's keepalive timeout.

Connection and Request Size Limits

<Connector port="8080" protocol="HTTP/1.1"
           maxConnections="10000"
           maxHttpHeaderSize="8192"
           maxPostSize="2097152"
           maxParameterCount="1000"/>

Parameter	Description	Default
maxConnections	NIO: max simultaneous connections	10000
maxHttpHeaderSize	Max request/response header size (bytes)	8192 (8KB)
maxPostSize	Max POST body size (bytes)	2097152 (2MB)
maxParameterCount	Max number of parameters	10000 (Tomcat 10.1)

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HTTPS Connector Configuration

Method 1: Java Keystore (JKS)

# Generate self-signed certificate (for testing)
keytool -genkey -alias tomcat \
  -keyalg RSA -keysize 2048 \
  -keystore /opt/tomcat/conf/keystore.jks \
  -validity 365 \
  -storepass changeit \
  -keypass changeit \
  -dname "CN=localhost, OU=Dev, O=MyCompany, L=Seoul, ST=Seoul, C=KR"

<!-- HTTPS Connector (JKS) -->
<Connector port="8443" protocol="org.apache.coyote.http11.Http11NioProtocol"
           maxThreads="150"
           SSLEnabled="true">
    <SSLHostConfig>
        <Certificate certificateKeystoreFile="conf/keystore.jks"
                     certificateKeystorePassword="changeit"
                     type="RSA"/>
    </SSLHostConfig>
</Connector>

Method 2: PEM Certificate (Let's Encrypt, etc.)

<Connector port="8443" protocol="org.apache.coyote.http11.Http11NioProtocol"
           maxThreads="150"
           SSLEnabled="true">
    <SSLHostConfig>
        <Certificate certificateFile="/etc/letsencrypt/live/example.com/cert.pem"
                     certificateKeyFile="/etc/letsencrypt/live/example.com/privkey.pem"
                     certificateChainFile="/etc/letsencrypt/live/example.com/chain.pem"
                     type="RSA"/>
    </SSLHostConfig>
</Connector>

Production recommendation: Rather than handling SSL directly in Tomcat, use Nginx/Apache for SSL termination and pass plain HTTP to Tomcat. This is much easier for performance and certificate management.

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Compression (Gzip) Configuration

<Connector port="8080" protocol="HTTP/1.1"
           compression="on"
           compressionMinSize="2048"
           compressibleMimeType="text/html,text/xml,text/plain,text/css,
                                 application/json,application/javascript"/>

Parameter	Description	Default
compression	on/off/force	off
compressionMinSize	Min response size to compress (bytes)	2048
compressibleMimeType	MIME types to compress	—

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Shared Thread Pool (Executor)

Use Executor when multiple connectors share a single thread pool.

<!-- Define shared thread pool -->
<Executor name="tomcatThreadPool"
          namePrefix="catalina-exec-"
          maxThreads="400"
          minSpareThreads="20"
          maxQueueSize="100"
          prestartminSpareThreads="true"/>

<!-- Connectors reference the Executor -->
<Connector port="8080" protocol="HTTP/1.1"
           executor="tomcatThreadPool"
           connectionTimeout="20000"/>

<Connector port="8443" protocol="org.apache.coyote.http11.Http11NioProtocol"
           executor="tomcatThreadPool"
           SSLEnabled="true">
    <SSLHostConfig>
        <Certificate certificateFile="conf/cert.pem"
                     certificateKeyFile="conf/key.pem"/>
    </SSLHostConfig>
</Connector>

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X-Forwarded-For Setup (Reverse Proxy)

When Tomcat is behind Nginx or Apache, pass the real client IP to Tomcat.

<!-- RemoteIpValve: treats X-Forwarded-For header as real IP -->
<Valve className="org.apache.catalina.valves.RemoteIpValve"
       remoteIpHeader="x-forwarded-for"
       proxiesHeader="x-forwarded-by"
       protocolHeader="x-forwarded-proto"
       internalProxies="127\.0\.0\.1|10\.\d+\.\d+\.\d+|192\.168\.\d+\.\d+"/>

With this Valve, request.getRemoteAddr() returns the actual client IP and request.isSecure() correctly indicates HTTPS.

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Connector Performance Tuning — Production Checklist

Small Server (2 CPU, 4GB RAM)

<Connector port="8080" protocol="HTTP/1.1"
           maxThreads="100"
           minSpareThreads="10"
           acceptCount="50"
           connectionTimeout="10000"
           keepAliveTimeout="10000"
           maxKeepAliveRequests="50"/>

Medium Server (48 CPU, 816GB RAM)

<Connector port="8080" protocol="HTTP/1.1"
           maxThreads="300"
           minSpareThreads="25"
           acceptCount="150"
           connectionTimeout="20000"
           keepAliveTimeout="15000"
           maxKeepAliveRequests="100"
           maxConnections="10000"/>

Large Server (16+ CPU, 32GB+ RAM)

<Executor name="tomcatThreadPool"
          maxThreads="800"
          minSpareThreads="50"
          maxQueueSize="200"/>

<Connector port="8080" protocol="org.apache.coyote.http11.Http11Nio2Protocol"
           executor="tomcatThreadPool"
           connectionTimeout="30000"
           maxConnections="20000"/>

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Summary

Setting	Parameter	Recommended Guideline
Max threads	maxThreads	CPU core count × 50 (IO-bound)
Accept queue	acceptCount	maxThreads × 0.5
Connection timeout	connectionTimeout	10000~20000ms
Thread sharing	Executor	Use when 2+ connectors exist
Real IP forwarding	RemoteIpValve	Required with reverse proxy
Compression	compression="on"	Recommended for JSON/HTML responses