1. SYNCHORNOUS AND
ASYNCHROUS EXECUTION
(WEBSERVERS)
EWERE DIAGBOYA

2. SYNCHRONOUS EXECUTION
• Synchronous processes wait for one to complete before the
next begins
• When you execute something synchronously, you wait for it to
finish before moving on to another task. When you execute
something asynchronously, you can move on to another task
before it finishes.

3. ASYNCHRONOUS EXECUTION
• Asynchronous refers to processes that do not depend on each
other's outcome, and can therefore occur on different threads
simultaneously
• Asynchronous communication is the exchange of messages,
such as among the hosts on a network or devices in a
computer, by reading and responding as schedules permit
rather than according to some clock that is synchronized for
both the sender and receiver or in real time. It is usually used
to describe communications in which data can be transmitted
intermittently rather than in a steady stream.

4. SYNCHRONOUS & ASYNCHRONOUS
EXECUTION
SYNCHRONOUS
• You are in a queue to get a movie ticket. You cannot get one until
everybody in front of you gets one, and the same applies to the
people queued behind you.
ASYNCHRONOUS
• You are in a restaurant with many other people. You order your food.
Other people can also order their food, they don't have to wait for
your food to be cooked and served to you before they can order. In
the kitchen restaurant workers are continuously cooking, serving,
and taking orders. People will get their food served as soon as it is
cooked.

5. SIDE NOTE
• Although asynchronous workflow processes might process
faster, synchronous processing is sometimes preferred. If a
calling application depends on information from the workflow
process, you should run the process synchronously to ensure
that the calling application gets the information it needs from
the process before the workflow finishes and the application
closes.

6. WHAT IS A WEB SERVER
• A web server is an information technology that processes
requests via HTTP, the basic network protocol used to
distribute information on the World Wide Web. The term can
refer either to the entire computer system, an appliance, or
specifically to the software that accepts and supervises the
HTTP requests

7. WEB SERVERS
• Lighttpd (asynchronous)
• Apache * (synchronous)
• Nginx * (asynchronous)
• IIS (Internet Information Services) (synchronous)
• AWS Lambda (event, asynchronous), AWS Kinesis
• Apache Tomcat

8. APACHE WEB SERVER
The Apache HTTP Server, colloquially called Apache is the world's
most used web server software. Originally based on the NCSA
HTTPd server, development of Apache began in early 1995 after
work on the NCSA code stalled. Apache played a key role in the
initial growth of the World Wide Web, quickly overtaking NCSA
HTTPd as the dominant HTTP server, and has remained most
popular since April 1996. In 2009, it became the first web server
software to serve more than 100 million websites.

9. APACHE WEB SERVER
Instead of implementing a single architecture, Apache provides a
variety of MultiProcessing Modules (MPMs), which allow Apache
to run in a process-based, hybrid (process and thread) or event-
hybrid mode, to better match the demands of each particular
infrastructure.
But Apache slows down under heavy load, because of the need to
spawn new processes, thus consuming more computer memory.
It also creates new threads that must compete with others for
access to memory and CPU. Apache will also refuse new
connections when traffic reaches the limit of processes
configured by the administrator.

10. • Load Balancing
• Loadable Dynamic Modules
• User and Session tracking
• Concurrent connection limiting
• Embedded Perl, PHP and Lua scripting
• Custom logging with rotation
• Concurrent connection limiting
• Request processing rate limiting
• Bandwidth throttling
• Server Side Includes
• IP address-based geolocation
FEATURES: APACHE WEB SERVER

11. COMPANIES USING APACHE

12. NGINX
• Nginx was created to be both a web server and a proxy server.
• Nginx was built to solve the C10k problem
• Uses asynchronous, non-blocking, event-driven connection
handling algorithm.
• This style of connection processing allows Nginx to scale
incredibly far with limited resources. Since the server is single-
threaded and processes are not spawned to handle each new
connection, the memory and CPU usage tends to stay relatively
consistent, even at times of heavy load.

13. FEATURES: NGINX
• Handling of static files, index files and auto-indexing
• Reverse proxy with caching
• Load balancing with in-band health checks
• FastCGI, SCGI, uWSGI support with caching
• Name- and IP address-based virtual servers
• IPv6-compatible
• HTTP/2 and SPDY protocol support
• FLV and MP4 streaming
• Web page access authentication
• URL rewriting
• Concurrent connection limiting
• Request processing rate limiting

14. • Quora.com
• Appnexus
• Wix
• Montana
• Mulesoft
• NASA
• Groupon
• Zendesk
COMPANIES USING NGINX

15. WEB SERVER USAGE
MAY 2014 JUNE 2014

16. CONTRASTS BETWEEN APACHE AND NGINX

17. MODULES: APACHE
• Apache's module system allows you to dynamically load or
unload modules to satisfy your needs during the course of
running the server.
• The Apache core is always present, while modules can be turned
on or off, adding or removing additional functionality and
hooking into the main server.
• Apache uses this functionality for a large variety tasks. Due to
the maturity of the platform, there is an extensive library of
modules available.
• These can be used to alter some of the core functionality of the
server, such as ‘mod_php’ which embeds a PHP interpreter into
each running worker.
• Modules are not limited to processing dynamic content, they can

18. MODULES: NGINX
• Nginx also implements a module system, but it is quite different from
the Apache system.
• In Nginx, modules are not dynamically loadable, so they must be
selected and compiled into the core software.
• While distributions' packages tend to include the most commonly
used modules, if you require a non-standard module, you will have to
build the server from source yourself.
• Nginx modules are still very useful though, and they allow you to
dictate what you want out of your server by only including the
functionality you intend to use.
• Nginx modules allow many of the same capabilities as Apache
modules. For instance, Nginx modules can provide proxying support,
compression, rate limiting, logging, rewriting, geolocation,

19. • Apache servers can handle static content using its conventional
file-based methods. The performance of these operations is
mainly a function of the MPM methods described above.
• Apache can also process dynamic content by embedding a
processor of the language in question into each of its worker
instances. This allows it to execute dynamic content within the
web server itself without having to rely on external components.
These dynamic processors can be enabled through the use of
dynamically loadable modules.
• Apache's ability to handle dynamic content internally means that
configuration of dynamic processing tends to be simpler.
Communication does not need to be coordinated with an
additional piece of software and modules can easily be swapped
STATIC & DYNAMIC CONTENT: NGINX:
APACHE

20. • Nginx does not have any ability to process dynamic content natively. To
handle PHP and other requests for dynamic content, Nginx must pass to
an external processor for execution and wait for the rendered content to
be sent back. The results can then be relayed to the client.
• For administrators, this means that communication must be configured
between Nginx and the processor over one of the protocols Nginx knows
how to speak (http, FastCGI, SCGI, uWSGI, memcache). This can
complicate things slightly, especially when trying to anticipate the
number of connections to allow, as an additional connection will be used
for each call to the processor.
• However, this method has some advantages as well. Since the dynamic
interpreter is not embedded in the worker process, its overhead will only
be present for dynamic content. Static content can be served in a
straight-forward manner and the interpreter will only be contacted when
STATIC & DYNAMIC CONTENT: NGINX

21. • Apache provides a variety of multi-processing modules (Apache
calls these MPMs) that dictate how client requests are handled.
Basically, this allows administrators to swap out its connection
handling architecture easily. These are:
• mpm_prefork (our model)
• mpm_worker
• mpm_event (new implementation)
CONNECTION HANDLING: APACHE

22. This processing module spawns processes with a single thread
each to handle request. Each child can handle a single connection
at a time. As long as the number of requests is fewer than the
number of processes, this MPM is very fast. However, performance
degrades quickly after the requests surpass the number of
processes, so this is not a good choice in many scenarios. Each
process has a significant impact on RAM consumption, so this
MPM is difficult to scale effectively. This may still be a good choice
though if used in conjunction with other components that are not
built with threads in mind. For instance, PHP is not thread-safe, so
this MPM is recommended as the only safe way of working with
‘mod_php’, the Apache module for processing these files.
CONNECTION HANDLING: APACHE:
MPM_PREFORK

23. This module is similar to the worker module in most situations,
but is optimized to handle keep-alive connections. When using the
worker MPM, a connection will hold a thread regardless of whether
a request is actively being made for as long as the connection is
kept alive. The event MPM handles keep alive connections by
setting aside dedicated threads for handling keep alive
connections and passing active requests off to other threads. This
keeps the module from getting bogged down by keep-alive
requests, allowing for faster execution. This was marked stable
with the release of Apache 2.4.
CONNECTION HANDLING: APACHE:
MPM_EVENT

24. • Nginx spawns worker processes, each of which can handle
thousands of connections. The worker processes accomplish this
by implementing a fast looping mechanism that continuously
checks for and processes events. Decoupling actual work from
connections allows each worker to concern itself with a connection
only when a new event has been triggered.
• Each of the connections handled by the worker are placed within
the event loop where they exist with other connections. Within the
loop, events are processed asynchronously, allowing work to be
handled in a non-blocking manner. When the connection closes, it
is removed from the loop.
CONNECTION HANDLING: NGINX

25. APACHE & NGINX IMPLEMENTATION
• Looking at the features of both technologies we see the strength
of one can complement the weakness of the other.
• For great performance both technologies could be used hand in
hand
• Placing Nginx in front of Apache helps to leverage the fast
processing ability to handle large number of concurrent requests
• While Nginx is a good load balancer and better in delivery of static
content, apache has the internal functionality of processing
dynamic content (e.g. PHP) better
• Dynamic requests can be proxied to Apache by Nginx
• Nginx returns the process page back to the user/client

26. APACHE & NGINX IMPLEMENTATION (STATIC &
DYNAMIC)
server {
server_name .example.com;
root /home/example.com/www;
[...]
location ~* .php.$ {
# Proxy all requests with an URI ending with .php*
# (includes PHP, PHP3, PHP4, PHP5...)
proxy_pass http://127.0.0.1:8080;
}
location / {
# Your other options here for static content
# for example cache control, alias...
expires 30d;
}
}
FILES THAT REQUIRE PROCESSING BEFORE BEING SENT TO THE CLIENT, SUCH AS PHP, PERL, AND
RUBY SCRIPTS, WILL BE SERVED BY APACHE

27. GOING CLOUD …..
• AWS; AWS Lambda
• A Lambda function and an event source are the core
components that you use when you work with AWS Lambda.
Event sources publish events, and a Lambda function is the
custom code that you write to process the events that
automatically gets invoked in response to events. In addition,
you can invoke your Lambda function directly over HTTPS or
using AWS SDKs.

28. THANK YOU