1 Server workloads

EC2 instances are most commonly used for server (rather than interactive) workloads:

• Network servers that listen for traffic on a port and service each incoming request, normally multi-threaded to permit multiple simultaneous clients.
• Batch processors that process tasks asynchronously as they arrive, often as messages in a queue or files in a folder.

Sometimes server programs are packaged and in an operating system’s package repository. Examples include common web, database, caching, mail and other servers. You will also encounter custom-written programs for solving particular business needs.

2 Characteristics

Regardless of functional purpose, server workloads have share common characteristics:

• Program runs non-interactively (or can be made to do so). This primarily means no prompted user input, and only log information to the console.
• Program doesn’t normally terminate. It will keep running until stopped.
• Configuration parameters either hard-coded, supplied on command-line or in config file(s).

3 Types

Compiled programs

written in any language for which a compiler exists on the target machine. Many possible original languages like C, C++, Golang, Haskell.

• Needs to be compiled for OS (Linux) and have required libraries statically linked or available as dynamic libraries on instance.

Bytecode-compiled programs

where the program is packaged by the developer and a runtime is used to execute it on the host. Often easiest as designed for portability.

Java

programs compiled to run on Java Runtime Environment (JRE). JRE installed from packages using yum/apt. Usually bundled as JAR file. Ideally should be a fat-JAR file that contains all required libraries.

.net

(in any supported language, often C# or VB). Similar idea to Java-based programs.

Interpreted programs

where the source code is executed by an interpreter at runtime. Examples: python, JavaScript.

4 Licensing

Even prior to the cloud’s inception, licensing has always been a very complicated topic. On the cloud, you will have to consider the licensing requirements for the software you use.

4.1 Ways to use software

Binary / executable

formats refer to machine readable copies of software that can execute but do not have the accompanying source code used to create them.

Source code

refers to human-readable instructions that can be compiled before running, interpreted at runtime, or both.

Remote usage

refers to network-accessible software-as-a-service that users connect to remotely.

4.2 Common licensing terms

Public domain

software has no restrictions attached to it. Although some software is public domain, most is covered by either a proprietary or a free license.

Proprietary

software is restricted and often governed by a license.

End User License Agreement (EULA)

governs the use of proprietary software, often subject to many restrictions.

Free software

is software licensed according to four essential freedoms:

1. Freedom to use
2. Freedom to understand/modify (meaning access to source code)
3. Freedom to distribute (or sell)
4. Freedom to distribute (or sell) modified versions.

Note that free is in the sense of “free speech” as opposed to “free cookies”. Free software can be bought and sold, whilst some proprietary software may be available at no cost.

Permissive

licenses allow you to modify software and then distribute or sell your modified version without corresponding source code.

Copyleft

refers to software whose free license prohibits making modifications and distributing them without corresponding source code.

Open source

is often mistakenly taken as a synonym of free software. Whilst having the source code is

FLOSS

meaning Free Libre Open Source Software is a catch-all term to encompass non-proprietary software.

subsection 1 shows the common free and open source software licenses and their relationship to each other.