Make sure you are using at least this level of IHS. Older levels have more performance concerns.
Release | Recommended level |
IHS 6.0 | any |
IHS 2.0.47.x | 2.0.47.1 or later |
IHS 2.0.42.x | 2.0.42.2-PQ85834 or later |
IHS 1.3.28.x | 1.3.28.1 or later |
IHS 1.3.26.x | 1.3.26.2 or later, along with e-fix PQ86671, which upgrades GSKit. |
GSKit levels used with IHS:
IHS 6.0.x | GSKit 7 |
IHS 2.0.47.x | GSKit 7 |
IHS 2.0.42.x | GSKit 5 |
IHS 1.3.28.x | GSKit 7 |
IHS 1.3.26.x | GSKit 5 |
The first tuning decision you'll need to make is determining how many simultaneous requests your IHS installation will need to support. Many other tuning decisions are dependent on this value.
For some IHS deployments, the amount of load on the web server is directly related to the typical business day, and may show a load pattern such as the following:
Simultaneous requests | 2000 | | | ********** | **** *** 1500 | ***** ** | **** *** | *** *** | * ** 1000 | * ** | * * | * * | * * 500 | * * | * * | ** * | *** *** 1 |*** ** Time of +------------------------------------------------------------- day 7am 8am 9am 10am 11am 12am 1pm 2pm 3pm 4pm 5pm
For other IHS customers, providing applications which are used in many time zones, load on the server varies much less during the day.
The maximum number of simultaneous connections must be based on the busiest part of the day. This maximum number of simultaneous connections is only loosely related to the number of users accessing the site. At any given moment, a single user can require anywhere from zero to four independent TCP connections.
The typical way to determine the maximum number of simultaneous connections is to monitor mod_status reports during the day until typical behavior is understood, or to use mod_mpmstats (IHS 2.0 and above for selected platforms).
Note that if the web server has not been configured to support enough simultaneous connections, one of the following messages will be logged to the web server error log and clients will experience delays accessing the server.
Windows [warn] Server ran out of threads to serve requests. Consider raising the ThreadsPerChild setting Linux and Unix [error] server reached MaxClients setting, consider raising the MaxClients setting
Check the error log for a message like this to determine if the IHS configuration needs to be changed.
Once the maximum number of simultaneous connections has been determined, add 25% as a safety factor. The next section discusses how to use this number in the web server configuration file.
Note: Setting of the KeepAliveTimeout can affect the apparent number of simultaneous requests being processed by the server. Increasing KeepAliveTimeout effectively reduces the number of threads available to service new inbound requests, and will result in a higher maximum number of simultaneous connections which must be supported by the web server. Decreasing KeepAliveTimeout can drive extra load on the server handling unnecessary TCP connection setup overhead. A setting of 5 to 10 seconds is reasonable for serving requests over high speed, low latency networks.
IBM HTTP Server on Windows has a Parent process and a single multi-threaded Child process.
Relevant config directives on Windows:
Recommended settings:
Directive | Value |
ThreadsPerChild | maximum number of simultaneous connections |
ThreadLimit | same as ThreadsPerChild (IHS 2.0 and above) |
On UNIX and Linux platforms, a running instance of IBM HTTP Server will consist of one single threaded Parent process which starts and maintains one or more multi-threaded Child processes. HTTP requests are received and processed by threads running in the Child processes. Each simulaneous request (TCP connection) consumes a thread. You need to use the appropriate configuration directives to control how many threads the server starts to handle requests and on UNIX and Linux, you can control how the threads are distributed amongst the Child processes.
Relevant config directives on UNIX platforms:The MaxSpareThreads and MinSpareThreads directives affect how the server autonomically reacts to server load. You can use these directives to instruct the server to automatically increase the number of Child processes when server load increases (subject to limits imposed by ServerLimit and MaxClients) and to decrease the number of Child processes when server load is low. This feature can be a useful for managing overall system memory utilization when your server is being used for tasks other than serving HTTP requests. IBM recommends disabling this autonomic behaviour by setting MaxSpareThreads to ....
Setting MaxSpareThreads to a relatively small value has a performance penalty: Extra CPU to terminate and create child processes. During normal operation, the load on the server may vary widely (e.g., from 150 busy threads to 450 busy threads). If MaxSpareThreads is smaller than this variance (e.g., 450-150=300), then IHS will terminate and create child processes frequently, resulting in reduced performance.
Recommended settings:
Directive | Value |
ThreadsPerChild | leave at the default value | MaxClients | maximum number of simultaneous connections, rounded up to an even multiple of ThreadsPerChild |
StartServers | 2 |
MinSpareThreads | same value as ThreadsPerChild |
MaxSpareThreads | same value as MaxClients |
ServerLimit | MaxClients divided by ThreadsPerChild |
ThreadLimit | ThreadsPerChild |
Note: ThreadLimit and ServerLimit need to appear before these other directives in the configuration file.
IHS 1.3 on Linux and Unix systems uses one single-threaded child process per concurrent connection.
Recommended settings:
Directive | Value |
MaxClients | maximum number of simultaneous connections |
MinSpareServers | 1 |
MaxSpareServers | same value as MaxClients |
StartServers | default value |
Refer to the previous section.
The default SSLCipherSpec ordering enables maximum strength SSL connections at a significant performance penalty. A much better performing and reasonably strong SSLCipherSpec configuration is given below.
With IHS 2.0 and above, Sendfile usage is disabled in the current default configuration files. This avoids some occasional platform-specific problems, but it also increases CPU utilization on platforms on which IHS supports it (Windows, AIX, Linux, and HP-UX).
If you enable sendfile usage on AIX, ensure that the
nbc_limit
setting displayed by the no
program is not too high for your system.
With IHS 2.0.42 and above, the default bin/envvars
file specifies
the setting MALLOCMULTIHEAP=considersize,heaps:8. This
enables a memory management scheme for the AIX heap library which is
better for multithreaded applications, and configures it to try to
minimize memory use and to use a moderate number of heaps. For
configurations with extensive heap operations (SSL or certain
third-party modules), CPU utilization can be lowered by changing this
setting to the following: MALLOCMULTIHEAP=true. This may
increase the memory usage slightly.
The Fast Response Cache Accelerator (FRCA, aka AFPA) is disabled in the current default configuration files because some common Windows extensions, such as Norton Antivirus, are not compatible with it. FRCA is a kernel resident micro HTTP server optimized for serving static, non-access protected files directly out of the file system. The use of FRCA can dramatically reduce CPU utilization in some configurations. FRCA cannot be used for serving content over HTTPS/SSL connections.
IBM HTTP Server supports some features and configuration directives that can have a severe impact on server performance. Use of these features should be avoided unless there are compelling reasons to enable them.
Performance penalty: Extra DNS lookups per request.
This is disabled by default in the sample IHS configuration files.
Performance penalty: Delays introduced in the request to contact RFC 1413 ident daemon possibly running on client machine
This is disabled by default in the sample IHS configuration files.
Performance penalty: Extra CPU and disk I/O to try to find the file type
This is disabled by default in the sample IHS configuration files.
Performance penalty: Extra CPU to compute MD5 hash of the response
This is disabled by default in the sample IHS configuration files.
Performance penalty: Extra CPU to terminate and create child processes
This is set to the optimal setting (0) in the sample IHS configuration files.
Performance penalty: Extra CPU and disk I/O to locate .htaccess files in directories where static files are served
.htaccess files are disabled in the sample IHS configuration files.
Detailed logging (SSLTrace, plug-in LogLevel=trace, GSKit trace, third-party module logging) is often enabled as part of problem diagnosis. When one or more of these traces is left enabled after the problem is resolved, CPU utilization is higher than normal.
Detailed logging is disabled in the sample IHS configuration files.
If the static files served by IHS are maintain by untrusted users, you may want to disable this option in the IHS configuration file, in order to prevent those untrusted users from creating symbolic links to private files that should not ordinarily be served by IHS. But disabling FollowSymLinks to prevent this problem will result in performance degradation since IHS then has to check every component of the pathname to determine if it is a symbolic link.
Following symbolic links is enabled in the sample IHS configuration files.
This directive is commonly modified as part of tuning the web server. There are advantages and disadvantages for different values of ThreadsPerChild:
This directive is commonly modified as part of tuning the web server to handle a greater client load (more concurrent TCP connections).
When MaxClients is increased, the value for MaxSpareThreads should be scaled up as well. Otherwise, extra CPU will be spent terminating and creating child processes when the load changes by a relatively small amount.
The use of the MaxConnections parameter in the WebSphere plug-in configuration is most effective when IHS 2.0 and above is used and there is a single IHS child process. However, there are other tradeoffs:
The selection of SSL cipher can dramatically affect performance of IBM HTTP Server. Stronger ciphers consume more CPU cycles than weaker ciphers. Of the strong ciphers, Triple-DES ciphers are the strongest but are far more expensive than the more commonly used 128 bit RC4 ciphers. Triple DES requires 3 passes (Encrypt/Decrypt/Encrypt) and was originally intended for compatibility with older DES devices. If the SAME key is used for each pass, you get DES and can communicate with older devices/programs, if you use DIFFERENT keys you get a very strong, but very expensive, cipher.
IBM HTTP Server supports the following SSL ciphers:
## shortname longname Meaning Note Strength ## ========= ======== ============= ==== ======== ## 27 SSL_DES_192_EDE3_CBC_WITH_MD5 Triple-DES (168 bit) * (stronger) ## 21 SSL_RC4_128_WITH_MD5 RC4 (128 bit) * ## 23 SSL_RC2_CBC_128_CBC_WITH_MD5 RC2 (128 bit) * | ## 26 SSL_DES_64_CBC_WITH_MD5 DES (56 bit) V ## 22 SSL_RC4_128_EXPORT40_WITH_MD5 RC4 (40 bit) ## 24 SSL_RC2_CBC_128_CBC_EXPORT40_WITH_MD5 RC2 (40 bit) (weaker) ## ## SSL V3 and TLSV1: ## ## shortname longname Meaning Note Strength ## ========= ======== ============= ==== ======== ## 3A SSL_RSA_WITH_3DES_EDE_CBC_SHA Triple-DES SHA (168 bit) * (stronger) ## 35 SSL_RSA_WITH_RC4_128_SHA RC4 SHA (128 bit) * ## 34 SSL_RSA_WITH_RC4_128_MD5 RC4 MD5 (128 bit) * | ## 35b TLS_RSA_WITH_AES_256_CBC_SHA AES SHA (128 bit) * ## 2F TLS_RSA_WITH_AES_128_CBC_SHA AES SHA (128 bit) * ## 39 SSL_RSA_WITH_DES_CBC_SHA DES SHA (56 bit) V ## 62 TLS_RSA_EXPORT1024_WITH_RC4_56_SHA RC4 SHA(56 Bit) ## 64 TLS_RSA_EXPORT1024_WITH_DES_CBC_SHA DES SHA(56 Bit) ## 33 SSL_RSA_EXPORT_WITH_RC4_40_MD5 RC4 MD5 (40 bit) ## 36 SSL_RSA_EXPORT_WITH_RC2_CBC_40_MD5 RC2 MD5 (40 bit) (weaker) ## 32 SSL_RSA_WITH_NULL_SHA ## 31 SSL_RSA_WITH_NULL_MD5 ## 30 SSL_NULL_WITH_NULL_NULL ## ## FIPS Approved NIST SSLV3 and TLSV1 (only available with SSLFIPSEnable): ## shortname longname Meaning Note Strength ## ========= ======== ============= ==== ======== ## 3A SSL_RSA_WITH_3DES_EDE_CBC_SHA Triple-DES SHA (168 bit) * (stronger) ## FF SSL_RSA_FIPS_WITH_3DES_EDE_CBC_SHA Triple-DES SHA (168 bit) * ## 35b TLS_RSA_WITH_AES_256_CBC_SHA AES SHA (128 bit) * ## 2F TLS_RSA_WITH_AES_128_CBC_SHA AES SHA (128 bit) * | ## 39 SSL_RSA_WITH_DES_CBC_SHA DES SHA (56 bit) V ## FE SSL_RSA_FIPS_WITH_DES_CBC_SHA DES SHA (56 bit) (weaker) ## ## ## * Note: Not supported in versions available ## outside North America. ##
When an SSL connection is established, the client and the server negotiate the cipher to use for the connection. By default, IBM HTTP Server attempts to use the strongest Triple-DES ciphers first. Use the SSLCipherSpec directive to rearrange the negotiation order. The following configuration directs the server to prefer strong 128 bit RC4 ciphers first and will provide a signicant performance improvement over the default configuration:
<VirtualHost *:443> Listen 443 SSLEnable Keyfile keyfile.kdb ## FIPS approved SSLV3 and TLSV1 128 bit Ciphers SSLCipherSpec 35b SSLCipherSpec 2F ## SSLV3 128 bit Ciphers SSLCipherSpec 34 SSLCipherSpec 35 SSLCipherSpec 2F ## SSLV2 128 bit Ciphers SSLCipherSpec 21 SSLCipherSpec 23 ## Triple DES Ciphers 168 bit Ciphers SSLCipherSpec 3A SSLCipherSpec FF SSLCipherSpec 27 </VirtualHost>
You can use the following LogFormat directive to view and log the SSL cipher negotiated for each connection:
LogFormat "%h %l %u %t \"%r\" %>s %b \"SSL=%{HTTPS}e\" \"%{HTTPS_CIPHER}e\" \"%{HTTPS_KEYSIZE}e\" \"%{HTTPS_SECRETKEYSIZE}e\"" ssl_common CustomLog logs/ssl_cipher.log ssl_common
This logformat will produce an output to the ssl_cipher.log that looks something like this:
127.0.0.1 - - [18/Feb/2005:10:02:05 -0500] "GET / HTTP/1.1" 200 1582 "SSL=ON" "SSL_RSA_WITH_RC4_128_MD5" "128" "128"
This assumes that you are using GSKit 5, version 5.0.5.92 or higher.
GSKit 5 ships both BSafe V6 and BSafe 5.2. BSafe V6 is the default configuration. The V6 version of BSafe is missing some AIX optimization and is therefore slower that BSafe V5.2, but V6 has functional enhancements: BSafe V5.2 does not support AES and RSA key lengths are restricted to a maximum of 1024 bits. If these restrictions are not important, then you can switch to BSafe 5.2.
The mechanism for switching differs between ppc and pwr architectures.
To determine if the machine is ppc or power architecture run the following commands:
gsk5isppc echo $?
If the result is 1, you're using ppc architecture.
In /usr/lib
the file libgsk5krsw.so
is a
soft link to /usr/opt/ibm/gskkm/lib/ppc/libgsk5krsw.so
.
To switch BSafe implementations, change this soft link to point at
/usr/opt/ibm/gskkm/lib/bsafev52ppc/libgsk5krsw.so
and
then restart IHS.
Example for ppc architecture:
rm /usr/lib/libgsk5krsw.so ln -s /usr/opt/ibm/gskkm/lib/bsafev52ppc/libgsk5krsw.so /usr/lib/libgsk5krsw.so
If the machine is pwr architecture then the soft link should be changed to:
ln -s /usr/opt/ibm/gskkm/lib/bsafev52pwr/libgsk5krsw.so /usr/lib/libgsk5krsw.so
The SSL CPU utilization will be lower with lower values of ThreadsPerChild. We recommend using a maximum of 100 if your server handles a lot of SSL traffic, so that the client load is spread among multiple child processes. (Note: This optimization is not possible on Windows, which supports only a single child process.)
Set this to the value true when there is significant SSL work-load, as this will result in better performance for the heap operations used by SSL processing.