How to Install Nextcloud 15 on Ubuntu 18.04

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Similar to Dropbox and Google Drive, Nextcloud is self-hosting software that allows you to share files, contacts, and calendars. But, unlike Dropbox and Google Drive, your files will be private and stored on your server instead of a third party server. Nextcloud is HIPAA and GDPR compliant, so your files will be encrypted along with the ability to audit. For this tutorial, we’ll be installing our Nextcloud instance on our Ubuntu 18.04 LTS server. Continue reading “How to Install Nextcloud 15 on Ubuntu 18.04”

How to Install phpMyAdmin on Ubuntu 18.04

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Working with a database can be intimidating at times, but phpMyAdmin can simplify tasks by providing a control panel to view or edit your MySQL or MariaDB database.  In this quick tutorial, we’ll show you how to install phpMyAdmin on an Ubuntu 18.04 server. Continue reading “How to Install phpMyAdmin on Ubuntu 18.04”

How to Setup Let’s Encrypt on Ubuntu 18.04

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Sites with SSL are needed more and more every day. It’s ubiquitious enforcement challenges website encryption and is even an effort that Google has taken up. Certbot and Let’s Encrypt are popular solutions for big and small businesses alike because of the ease of implementation.  Certbot is a software client that can be downloaded on a server, like our Ubuntu 18.04, to install and auto-renew SSLs. It obtains these SSLs by working with the well known SSL provider called Let’s Encrypt. In this tutorial, we’ll be showing you a swift way of getting HTTPS enabled on your site.  Let’s get started! Continue reading “How to Setup Let’s Encrypt on Ubuntu 18.04”

How to Install Apache on a Windows Server

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When looking to host web sites or services from a Windows server, there are several options to consider. It is worth reviewing the strengths and weaknesses of each server type to determine which one is most likely to meet your particular needs before you spend the time installing and configuring a web service.

Some of the most common web servers available for Windows services are Tomcat, Microsoft IIS (Internet Information Services), and of course the Apache server. Many server owners will choose to use a control panel which manages most of the common tasks usually needed to administer a web server such as e-mail and firewall configuration.

At LiquidWeb, that option means you’re using one of our Fully Managed Windows Servers with Plesk. Alternately, some administrators who need more flexibility choose one of our Core or Self-Managed Windows Servers. This article is intended for the latter type of server with no Plesk (or other) server management control panel.

Pre-Flight Check

This guide was written for a 64-bit Windows server since a modern server is more likely to utilize that platform. There are also a few potential issues with Apache on a Win32 systems (non 64-bit) which you should be aware of and can be reviewed here.


Downloading Apache:

While there are several mirrors to choose from for downloading the pre-compiled Apache binaries for windows, we’ll be using ApacheHaus for our purposes.

Download Here:

Apache 2.4.38 with SSL

(This is the 64-bit version with OpenSSL version 1.1.1a included). If you would like to utilize an alternate version they are listed here:

Available Versions Page

 

Install Apache on Windows

We will assume that you have installed all the latest available updates for your version of Windows. If not, it is very important to do so now to avoid unexpected issues. These instructions are specifically adapted from the directions provided by ApacheHaus where we obtained the binary package. You may find the entire document in the extracted Apache folder under the file “readme_first.html”.

 

Visual C++ Installation

Before installing Apache, we first need to install the below package. Once it has been installed, it is often a good idea to restart the system to ensure any remaining changes requiring a restart are completed.

  1. Download the Visual C++ 2008 Redistributable Package and install it. It is located here.
     
    Note:
    Download the x64 version for 64 bit systems.
  2. Restart (optional but recommended).

Apache Installation

  1. Extract the compressed Apache download. While you can extract it to any directory it is a best practice to extract it to the root directory of the drive it is located on (our example folder is located in C:\Apache24). This is the location we will be using for these instructions. Please note that once installed you can see Apache’s base path by opening the configuration file and checking the “ServerRoot” directive).apache_extract
  2. Open an “Administrator” command prompt. (Click the Windows “Start” icon, then type “cmd”. Right-click the “Command Prompt” item which appears, and select “Run As Administrator.”)
  3. Change to the installation directory (For our purposes C:\Apache24\bin).
  4. Run the program httpd.exe.
  5. You will likely notice a dialogue box from the Windows Firewall noting that some features are being blocked. If this appears, place a checkmark in “Private Networks…” as well as “Public Networks…”, and then click “Allow access.”
  6. As noted in the ApacheHaus instructions:

“You can now test your installation by opening up your Web Browser and typing in the address: http://localhost

If everything is working properly, you should see the Apache Haus’ test page.“

apache_test_page

To shut down the new Apache server instance, you can go back to the Command Prompt and press “Control-C”.

  1. Now that you have confirmed the Apache server is working and shut it down, you are ready to install Apache as a system service.
  2. In your Command Prompt window, enter (or paste) the following command:

httpd.exe -k install -n "Apache HTTP Server"

Output:

Installing the 'Apache HTTP Server' service
The 'Apache HTTP Server' service is successfully installed.
Testing httpd.conf....
Errors reported here must be corrected before the service can be started.
(this line should be blank)

apache_service

  1. From your Command Prompt window enter in the following command and press ‘Enter.’services.msc

Look for the service “Apache HTTP Server.” Looking towards the left of that line you should see “Automatic.” If you do not, double-click the line and change the Startup Type to “Automatic.”

  1. Restart your server and open a web browser once you are logged back in. Go to this page in the browser’s URL bar: http://localhost/

Configure Windows’ Firewall

To allow connections from the Internet to your new web server, you will need to configure a Windows Firewall rule to do so. Follow these steps:

  1.  Click the “Windows Start” button, and enter “firewall.” Click the “Windows Firewall With Advanced Security” item.
  2. Click “New Rule” on the right-hand sidebar.firewall1
  3. Select “Port,” and click Next. Select the radio button next to “Specific remote ports:” Enter the following into the input box: 80, 443, 8080

    firewall2

  4. Click Next, then select the radio button next to “Allow the connection.”
  5. Click Next, ensure all the boxes on the next page are checked, then click Next again.
  6. For the “name” section enter something descriptive enough that you will be able to recognize the rule’s purpose later such as: “Allow Incoming Apache Traffic.”
  7. Click “finish.”

    firewall3

  8. Try connecting to your server’s IP address from a device other than the one you are using to connect to the server right now. Open a browser and enter the IP address of your server. For example http://192.168.1.21/. You should see the test webpage.
  9. For now, go back to the windows firewall and right-click the new rule you created under the “Inbound Rules” section. Click “Disable Rule.” This will block any incoming connections until you have removed or renamed the default test page as it exposes too much information about the server to the Internet. Once you are ready to start serving your new web pages, re-enable that firewall rules, and they should be reachable from the Internet again.

That’s it! You now have the Apache Web Server installed on your Windows server. From here you’ll likely want to install some Apache modules. Almost certainly you will need to install the PHP module for Apache, as well as MySQL. Doing so is beyond the scope of this tutorial; however, you should be able to find a variety of instructions by searching “How to Install PHP (or other) Apache module on Windows server,” or similar at your favorite search engine.

 

Install and Configure Mod_Security on Ubuntu 16.04 Server

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Mod_security, also commonly called Modsec for short, is a powerful WAF (Web Application Firewall) that integrates directly into Apache’s module system. This direct integration allows the security module to intercept traffic at the earliest stages of a request. Early detection is crucial for blocking malicious requests before they are passed along to web applications hosted by Apache web sites. This provides and extra layer of protection against common threats a server faces. This article will explore the installation of mod_security along with the CRS (Core Rule Set) in a Ubuntu 16.04 LTS Server running Apache 2.4. Continue reading “Install and Configure Mod_Security on Ubuntu 16.04 Server”

How to Install PHP 7.2 on Ubuntu 16.04

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Using PHP 7.2 on an Ubuntu server is highly recommended over previous PHP versions for several reasons, first being security. Active Support for PHP 7.2 goes until November 30th, 2019 and Security Support until Nov 30, 2020. Older versions like 7.0 and anything 5.6 and below are no longer getting any support and can leave open security holes on a server if they are not replaced. Another main reason to upgrade is the big performance increase over previous versions when PHP 7.2 is installed and is using the OPcache module.  This can greatly decrease the time it takes for your webpage to load! If you are developing a site locally or launching it on one of Liquid Web’s Ubuntu VPS or Dedicated Servers, using PHP 7.2 or newer would be the way to go.

Continue reading “How to Install PHP 7.2 on Ubuntu 16.04”

Install Poweradmin on Ubuntu 16.04

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What is Poweradmin?

Poweradmin is a web-based graphical user interface to interact with PowerDNS. It is released under the open source GPL license. It makes it easy to create and edit zone files and interacts directly with the SQL server. Poweradmin has full support for most PowerDNS features, including all zone types (master, native and slave), supermasters, for automatic provisioning of slave zones and full support for A, AAAA, CNAME, HINFO, MX, NS, PTR, SOA, SRV and TXT record types, validation against RFC’s. It also has user and permission management setup for controlling user permissions with templates.  In this tutorial, we’ll be showing you how to install and configure Poweradmin as well as some records.

Continue reading “Install Poweradmin on Ubuntu 16.04”

Apache Performance Tuning: Configuring MPM Directives

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Our previous article in this series focused on defining and fitting MPM to match your environment.  Building off of our last tutorial we will be discussing specific details on how to adjust the previously mentioned Apache configuration directives on the various types of Liquid Web servers

Continue reading “Apache Performance Tuning: Configuring MPM Directives”

Apache Performance Tuning: MPM Directives

Reading Time: 12 minutesHow directives behave and which directives are mainly available hinges on the loaded MPM. As discussed in our previous series, MPM is short for MultiProcess Modules, and they determine the basis for how Apache addresses multiprocessing. Using our last article on Apache MPM Modules as a springboard, we will use this section to cover the following subsections:

Each part will focus on how the directives affect performance for their respective MPM and some common considerations that should be assessed when optimizing Apache with those specific MPMs.

Note:
Be sure to review this article in its entirety as the universal directives operate in the same manner regardless of the MPM chosen.

 

General Optimization

IfModule

An important directive to learn when working with Apache servers is the IfModule conditional statement. There are two parts to the IfModule statement. A beginning, which also accepts a module name or module source file name, as well as a closing statement. When the provided module is loaded into Apache, then all directives between the beginning IfModule statement and the closing IfModule statement are also read into the Apache running configuration. Please review the provided example below for further clarification:

 

<ifModule mpm_prefork_module>
MaxSpareServers 16
</ifModule>
Timeout 60
The above example defines the MaxSpareServers directive only when loaded by mpm_prefork_module. The Timeout directive is applied every time due to it being outside of the IfModule closing statement.

 

IfModule statements are used to maintain compatibility within Apache configuration between module changes. Maintaining compatibility is done by grouping directives into IfModule statements, so they are only used when the required module is loaded. Ensuring a syntactically correct configuration file even when swapping modules.

Rule of Thumb:
Appropriately wrapping everything in an IfModule statement is a best practice standard with Apache and should be adhered to for superior compatibility in config files.

Timeout

The numerical value of seconds Apache waits for all common I/O events. Apache will abandon requests fail to complete before the provided Timeout value.

Determining the right Timeout depends on both traffic habits and hosted applications. Ideally, Timeout should be as low as possible while still allowing the vast majority of regular traffic to operate without issue. Large timeouts, those above 1 minute, open the server to SlowLoris style DOS attacks and foster a long wait in the browser when it encounters a problem. Lower timeouts allow Apache to recover from errant stuck connections quickly. It becomes necessary to strike a balance between the two extremes.

Tip:
Avoid increasing the global Timeout when addressing issues with a single script, or user, that requires a long Timeout. Problems can usually be resolved by a .htaccess file or include file to increase the Timeout directive for that specific script.

KeepAlive

KeepAliveA simple on|off toggle enables the KeepAlive protocols with supported browsers. The KeepAlive feature can provide as much as a 50% reductions in latency, significantly boosting the performance of Apache. KeepAlive accomplishes this by reusing the same initial connections a browser creates when connecting to Apache for all follow-up requests which occur within a short period.

KeepAlive is a powerful feature and in general, should be enabled in most situations. It works great for reducing some of the CPU and Network overhead with modern element heavy websites. For example, an easy way to visualize KeepAlive is with the “hold the door” phrase. Imagine a queue of people entering a building through a single doorway. Each person is required to open the door, walk through it, then close the door before the next person does the same process. Mostly, that’s how Apache works without KeepAlive. When enabled, the door stays open until all the people in line are through the door before it closes again.

Two additional related directives also govern KeepAlive. MaxKeepAliveRequests and KeepAliveTimeout. Discussed in the next section, each one plays a vital role in fine-tuning of the KeepAlive directive.

 

MaxKeepAliveRequests

Sets a limit on the number of requests an individual KeepAlive connection is permitted to handle. Once reached, Apache forces the connection to terminate, and creates a new one for any additional requests.

Determining an ideal setting here is open to interpretation. Generally, you want this value to be at least as high as the largest count of elements (HTML, Text, CSS, Images, Etc..) served by the most heavily trafficked pages on the server.

Rule-of-Thumb:
MaxKeepAliveRequestsSet MaxKeepAliveRequests to double that of the largest count of elements on common pages. (Services like webpagetest.org or gtmetrix.com can count elements on a page).

KeepAliveTimeout

This directive is measured in seconds and will remain idle waiting for additional requests from its initiator. Since these types of connections are only accessible to their initiator, we want to keep KeepAliveTimeout very low. A low value prevents too many KeepAlive connections from locking out new visitors due to connection priority.

Tip:
KeepAliveTimoutA large MaxKeepAliveRequests directive with a very low KeepAliveTimeout allows active visitors to reuse connections while also quickly recovering threads from idle visitors.
Configuration: Set MaxKeepAliveRequests to 500+, Set KeepAliveTimeout to 2
Requirements: Works best on MPM Event.


MPM Event/Worker Optimization

This section details the use and performance considerations that are essential when running Worker based MPMs, including both MPM Event and MPM Worker. These MPMs are considered multi-threaded solutions and some directives behave differently based on the loaded MPM. The information provided in this section is only a portion about Worker based MPMs.

Note:
In Worker based MPMs: ServerLimit, ThreadsPerChild, and MaxRequestWorkers are intrinsically linked with each other. It is essential to understand the role of each one and how changing one affects the others. The following directives govern the fine-tuning of the thread handling capabilities of Apache web servers.

MPM Worker and MPM Event

The two modules, MPM Event, and MPM Worker for most intents and purposes operate identically. The difference is apparent in the way each handles KeepAlive requests. The MPM Worker locks threads for the duration of the KeepAlive process and directly affects the number of available threads able to handle new requests. The MPM Event uses a Listener thread for each child. These Listener threads handle standard requests, and KeepAlive requests alike meaning thread locking will not reduce the capacity of the server. Without thread locking, MPM Event is the superior choice but only in Apache 2.4. Before Apache 2.4 the MPM Event was unstable and prone to problems.

ServerLimit

ServerLimit represents the upper limit of children Apache is allowed. The practical usage for ServerLimit is creating a hard ceiling in Apache to protect against input errors with MaxRequestWorkers. The cap prevents spawning vastly more children than a system can handle, resulting in downtime, revenue loss, reputation loss or even data loss.ServerLimit

ServerLimit ties in directly with the thrashing point discussed earlier in this article. The thrashing point is the maximum number of children Apache can run before memory usage tips the scale into perpetual swap. Match the ServerLimit to the calculated thrashing point to safeguard the server.

 

ThreadsPerChild

Used to define the limit of threads that each Apache child can manage. Every thread running can handle a single request. The default of 25 works well for most cases and is a fair balance between children and threads.ThreadsPerChild

There is an upper limit on this directive as well, and the limit is controlled by the ThreadLimit directive, which defaults to 64 threads. The adjustments to increase ThreadsPerChild past 64 threads also need to be made to ThreadLimit.

Increasing this value allows each child to handle more requests keeping memory consumption down while allowing a larger MaxRequestWorkers directive. A key benefit of running more threads within each child is shared memory cache access. Threads from one child cannot access caches from another child. Boosting the number of threads per child squeezes out more performance due to this sharing of cache data. The major downside for increased threads per child occurs during child recycling. The capacity of the server is diminished by the number of threads configured for each child when that child process is eventually recycled (graceful restart).

MPM Event/Worker

Inversely the opposite reaction is achieved by lowering ThreadsPerChild. Fewer threads per child require more children to run an equal amount of MaxRequestWorkers. Since children are full copies of Apache, this increases Apache’s overall memory footprint but reduces the impact when recycling children. Fewer threads mean fewer potential “stuck” threads during the recycle procedure, keeping the higher capacity of requests available overall children. Having fewer threads per child provides increased shared memory isolation. For instance, dropping ThreadsPerChild to 1 gives the same request isolation of MPM Prefork but also inherits its massive performance tax as well, requiring one child per one request.

Tip:
When setting ThreadsPerChild always consider the server environment and hardware.

  • A memory-heavy shared server hosting numerous independent accounts might opt for a lower ThreadsPerChild, reducing the potential impact of one user affecting another.
  • A dedicated Apache server in a high capacity load balanced configuration can choose to increase ThreadsPerChild significantly for a better overall performance of each thread.

ThreadLimit

Used to set the maximum value of ThreadsPerChild. This directive is a hard ceiling for ThreadsPerChild. It helps protect against typographical errors with the ThreadLimit
ThreadsPerChild directive which could quickly spin a server out of control if too many threads are allowed due to an input error. This setting need to be adjusted in some high-end servers when the system needs more than the default of 64 threads per child.

MaxRequestWorkers / MaxClients

The directive sets the limit for active worker threads across all running children and acts as a soft ceiling with ServerLimit taking control as the hard limit. When the number of total running threads has reached or exceeded MaxRequestWorkers, Apache no longer spawns new children.MaxRequestWorkers/MaxClients

Determining the MaxRequestWorkers is a critical part of server optimization. An optimal setting is based on several changing variables. This means its configuration needs to be reevaluated and tailored periodically over time, changed by watching traffic habits and system resource usage. The Apache status Scoreboard is an effective tool for analysis of Apache performance.

 

It is typical of Worker based MPM systems to run an isolated third-party PHP handler like Mod_fcgid, PHP-FPM, and mod_lsapi. These modules are responsibleMPM Event/Worker2

for processing PHP code outside of Apache and frees up Apache to handle all other non-PHP requests such as HTML, TEXT, CSS, Images, etc… These requests are far less taxing on server resources which allows Apache to handle larger volumes of requests, such as those beyond 400 MaxRequestWorkers.

MinSpareThreads

The least number of Threads that should remain open, waiting for new requests. MinSpareThreads is a multiple of ThreadsPerChild and cannot exceed MaxSpareThreads, though it can match it.

Rule-of-Thumb:
Set MinSpareThreads to equal 50% of MaxRequestWorkers.

Spare threads are idle workers threads. These threads are merely waiting for new incoming requests and are governed by the Apache child process that spawned them. If there are less available threads than MinSpareThreads, The Apache parent will generate a new child with another ThreadsPerChild worth of threads.

MinSpareThreads

MaxSpareThreads

This directive governs the total number of idle threads allowed on the server across all children. Any threads above this limit direct their parent to shut down to reduce memory consumption during off-peak hours.MaxSpareThreads

Having a limit to the number of idle open threads is excellent for smaller servers with hardware constraints. However, it mostly unneeded on today’s modernizing hardware.

Tip:
Configuring Apache as an open throttle is a high-performance configuration for servers with significant RAM and multiple CPU cores. When running the open throttle configuration, all available threads become available at all time. Apache’s memory usage will stay near its peak at all times, a side effect due to running all the configured children into memory preemptively. This configuration will produce the best possible response times from Apache by maintaining persistent open connections ready to do work and removing the overhead of spawning new processes in response to traffic surges.

Configuration: Match both MinSpareThreads and MaxSpareThreads to MaxRequestWorkers.

Requirements: Make sure there is enough server RAM to run all MaxRequestWorkers at once.

StartServers

This directive governs the initial amount of children the Apache Parent process spawns when the Apache service is started or restarted. This is commonly left unchanged since Apache continuously checks the current running children in conjunction with ThreadsPerChild and compare it to MinSpareThreads to determine if more children get forked. This process is repeated perpetually, with a doubling of new children on each iteration, until MinSpareThreads is satisfied.

Rule-of-Thumb:
StartServerManually calculating StartServers is done by dividing MaxRequestWorkers by ThreadsPerChild, rounding down to the nearest whole number. This process forces all children to be created without delay at startup and begins handling requests immediately. This aspect is especially useful in modern Apache servers which require periodic restarts to load in directive changes.

MaxConnectionsPerChild / MaxRequestsPerChild

The number of requests a single Apache child process can handle equals a cumulative total on the child server across all threads it controls. Each request handled by a thread counts toward this limit to its parent. Once the child server has reached its limit, the child is then recycled.
This directive is a stop-gap for accidental memory leaks. Some code executed through Apache threads may contain memory leaks. Leaked memory are portions of memory that subprocess failed to release properly, so they are inaccessible to any outside processes. The longer a leaking program is left running, the more memory it will leak. Setting a MaxConnectionsPerChild limit is a specific method for assuring Apache is periodically recycling programs to reduce the impact of leaked memory on the system. When using external code handlers like Mod_fcgid, PHP-FPM or mod_lsapi, it becomes necessary to set MaxConnectionsPerChild to 0 (unlimited), doing so prevents periodic error pages caused by Apache terminating threads prematurely.

Rule-of-Thumb:
MaxConnectionsPerChild/MaxRequestsPerChild If the server encounters a memory leak never set the MaxConnectionsPerChild / MaxRequestsPerChild too low, instead start with 10,000 and reduce it incrementally.


 

MPM Prefork Optimization

This MPM Prefork section details the use and performance considerations for various directives when running this module. This MPM is a non-threaded multi-processor designed for compatibility. It consists of a single Apache parent process, which is used to govern all new Apache processes also known as children. The following directives show how Apache is capable of performance tuning when using MPM Prefork. Unlike Worker based MPMs, optimizing MPM Prefork is generally simple and straightforward. There is a 1:1 ratio of Apache processes to incoming requests. However, MPM Prefork does not scale well with hardware and the more traffic it encounters, the more hardware it will need to keep up with the pace. It should be noted that some directives behave differently based on which MPM is loaded. The information provided in this section is only the portion about MPM Prefork.

MaxRequestWorkers / MaxClients

Used to control the upper limit of children that the Apache parent server is allowed to have in memory at one time. These children (also called workers) handle requests on a 1:1 ratio. This translates into the maximum number of simultaneous requests the server can handle.

MaxRequestWorkers / MaxClientsIf this directive is too low, Apache under-utilizes the available hardware which translates to wasted money and long delays in page load times during peak hours. Alternatively, if this directive is too high, Apache outpaces the underlying hardware sending the system into thrashing (link to thrashing article) scenario which can lead to server crashes and potential data loss.

 

MinSpareServers

This directive defines a minimum number of spare children the Apache parent process can maintain in its memory. An additional server is a preforked idle Apache child that is ready to respond to a new incoming request. Having idle children waiting for new requests is essential for providing the fastest server response times. When the total idle children on the server drop below this value, a new child is preforked at the rate of one per second until this directive is satisfied. The “one per second” rule is in place to prevent surges of the creation process that overload the server, however, this failsafe comes at a cost. The one per second spawn rate is particularly slow when it comes to handling page requests. So it’s highly beneficial to make sure enough children are preforked and ready to handle incoming requests.

 

Rule of Thumb:
MinSpareServers Default settingNever set this to zero. Setting this to 25% of MaxRequestWorkers ensures plenty resources are ready and waiting for requests.

MaxSpareServers

MasSpareServers controls the maximum number of idle Apache child servers running at one time. An idle child is one which is not currently handling a request but waiting for a new request. When there are more than MaxSpareServers idle children, Apache kills off the excess.

If the MaxSpareServers value is less than MinSpareServers, Apache will automatically adjust MaxSpareServers to equal MinSpareServers plus one.

Like with MinSpareServers, this value should always be altered with available server resources in mind.

Rule of Thumb:

MaxSpareServersSet this to double the value of MinSpareServers.

Tip:
Configuring Apache as an open throttle is a high-performance configuration for servers with significant RAM and multiple CPU cores. When running the open throttle configuration, all available Apache children become available at all times. As a side effect of running open throttle, the Apache memory usage will stay near its peak at all times, due to running all the configured children into memory preemptively. This configuration will produce the best possible response times by maintaining persistent open connections. Furthermore, in response to traffic surges, it removes the overhead that comes from spawning new processes.
Configuration: Match both MinSpareServers and MaxSpareServers to MaxRequestWorkers.
Requirements: Make sure there is enough server RAM to run all MaxRequestWorkers at once.

StartServers

Created at startup, are the initial amount of Apache child servers.

This seldom changed directive only impacts Apache startup and restart processes. Generally not altered because Apache uses internal logic to work out how many child servers should be running.

Many modern servers periodically restart Apache to address configuration changes, rotate log files or other internal processes. When this occurs during a high load traffic surge, every bit of downtime matters. You can manually set the StartServers directive to mirror that of your MinSpareServers to shave off time from the Apache startup.

Rule of Thumb:
StartServersThe StartServers directive should mirror that of MinSpareServers.

 

ServerLimit

The ServerLimit directive represents the upper limit of MaxRequestWorkers. This setting is generally used as a safeguard or ceiling against input errors when modifying MaxRequestWorkers.ServerLimit Default Setting

It becomes necessary to adjusted ServerLimit when the server is expected to handle more than the default of 256 requests simultaneously.

ServerLimit ties in directly with the thrashing point. The thrashing point is the maximum number of children Apache can run before memory usage tips the scale into perpetual swap. Match the ServerLimit to the calculated thrashing point to safeguard the server.

Note:
Increasing ServerLimit is not recommended with MPM Prefork. Running more than 256 simultaneous requests is hardware intensive when using the MPM Prefork module.

ThreadsPerChild Default Settings

MaxConnectionsPerChild / MaxRequestsPerChild

This directive equals the number of requests a single Apache child server can handle.

This directive is a stop-gap for accidental memory leaks. Code executed through Apache may contain faults which leak memory. These leaks add up over time making less and less of the shared memory pool of the child usable. The way to recover from leaked memory is to recycle the affected Apache child process. Setting a MaxConnectionsPerChild limit will protect from this type of memory leakage.

Note:
MaxConnectionsPerChild/MaxRequestsPerChild Rule-of-Thumb: Never set this too low. If the server encounters memory leak issues start with 10,000 and reduce incrementally.