SRE is an exciting field. As mentioned earlier, it has evolved from a long line of roles and, as it is a relatively new field, its definition is steadily changing. SRE is an extension and evolution of many past concepts and, as such, concepts relevant to SRE apply to many roles, including but not exclusive to, backend engineering, DevOps, systems engineering, systems administration, operations, and so on. Depending on the company, these roles can involve very similar or very different responsibilities. The point is that, no matter what your job title is, you can apply SRE principles to your role.

In an attempt to define the field, we can learn a lot from its full name, Site Reliability Engineering:

Merging these three definitions, we get something like, "The field focused on working artfully to bring about a website that performs consistently well." While this definition could use some brushing up, it suits our needs for now. If you work, or know people who work, in the web development or software engineering world and you ask them what SRE means, then they may ask you, "Isn't that like X?" To someone from that background, X might be "DevOps," "ops," "platform engineering," "infrastructure engineering," "24/7 engineering," "a sysadmin," and so on.

This variation of answers presents the first problem we will see throughout this book: every organization is different. SRE's primary goal is making a website perform consistently according to our previous definition, which is difficult because it is dependent on the organization, the business around that organization, and the website's (or product's) requirements. One of the primary goals of this book is to present a framework that you can apply even if you do not belong to an organization with any of the aforementioned roles. The framework should be effective if you work for yourself, and it should also work if you are employed by some gigantic international multi-headed Hydra organization, and anything in between.

I worked as an SRE in 2016 for Hillary for America. It was the lead organization (but definitely not the only one) working to help to elect Hillary Clinton as President of the United States of America. We were not successful, and while this example immediately dates this book, I found it to have the most concrete separation of concerns between the parts of a website that I have ever worked on. The organization was hyper-focused on one goal (electing Hillary Clinton as president), so it had a very explicit list of goals that made my job a lot easier.

There were many separate parts of the campaign that the technology team worked on, including a mobile application, different websites, data pipelines, and large databases. To keep this simple though, and to explain what I mean by a separation of concerns, let me use three separate websites that we built and maintained as an example:

Figure 1: Screenshots of different parts of hillaryclinton.com, courtesy of the Hillary for America design team. From left to right: the header on the home page, a page about Nevada, a page about Hillary's policies, Hillary's home page in Spanish, the campaign blog, and the donate page.

The home page was a general landing page. It needed to be available during the hours that people in North America were awake (as our target audience was mostly based in the United States), but very few people visited the home page unless driven there.

The main reason you would go to https://www.hillaryclinton.com/ was if you were sent there, not because it was part of your daily browsing like you would visit Twitter or Reddit. Surrogates speaking at rallies, on the radio, or on television supporting Hillary Clinton would often say things like, "Go to hillaryclinton.com now to sign up," or "hillaryclinton.com has more details on her policies on this topic." A five-minute outage here and there was OK, because of this semipredictable traffic spike, but like many media organizations, there were no guarantees of when a large spike of traffic would occur.

The donate page always needed to be up. According to our product team and senior leadership, the donate page's availability was priority number one. If people could not give money, then the campaign might not be able to pay people's salaries or get the candidate to her speaking engagements. The donation site was not the only way that the campaign made money, but it was a significant source of income.

The voter registration page only needed to be fully available when there was an election coming soon. This was because the page let people say they were going to vote for Hillary Clinton and find their nearest polling location. While the donate page needed to be available for the majority of the campaign (May 2015 through to November 2016), the voter registration page only really needed to be available during the lead up to the primary election (September through to November of 2016). If we had built the voter registration page earlier in the election, it also would have been needed in the days leading up to the primaries, but then only for states that were voting on those days. Primary elections are a precursor to the general election and happen from February to June, with different states voting on different days.

The key here is that different websites and features have different requirements and a different definition of being reliable. Nothing will ever be perfect, nor is 100% uptime achievable on the internet, because things are always breaking. So, all we can do is figure out what sort of failures we might have and optimize our product to be resilient in a way that is useful for us. SRE isn't just the analysis of systems; it is also the architecting and building of systems so that they meet the requirements of the product.

Often, the job of someone working in SRE is to take in reliability requirements for software, and its infrastructure, and then figure out how to make the infrastructure meet those requirements. Steps toward this often require figuring out if existing infrastructure is meeting those needs, collaborating with teams (or people writing software that will run on the infrastructure), evaluating external tools, or just designing and writing what you need yourself.

As I mentioned at the beginning of the chapter, an SRE role can be very diverse. The requirements of an SRE position at a Fortune 500 company can be very different to those of a 20-person video game company. The role could be different at a bank in the USA from a role at a bank on the other side of the world. This is because the organization is different. For smaller organizations, someone working as an SRE may handle everything in the organization related to infrastructure and reliability. On the other hand, larger organizations may have multiple teams of SREs working with many diverse teams of developers. The role between two different banks could be different because of each bank's needs.

A local bank may only need someone to improve the reliability of tools for people who work for the bank, while a much larger bank in London may need someone who can make sure their bank's systems can make trades at very high speeds with the London Stock Exchange or support millions of individual customers. This book will provide a structure for anyone interested in becoming an SRE. The goal is to empower you, no matter your background or current situation. It will not be a panacea but will provide a knowledge base and a framework for making sites more reliable and moving your career forwards.

I worked as an SRE at Google for four years, and that is where I started specializing, moving away from being a full stack engineer, and instead considering myself an SRE. Google had lots of internal education courses, and when I left, I found it difficult to continue my education. I also quickly discovered that SRE at Google is a very different beast than SRE at much smaller organizations. I decided to write this book for people interested in starting with SRE or applying it to organizations that are much smaller than Google.

To do this, the book is broken up into two parts. The first eight chapters walk through the hierarchy of reliability. This hierarchy was originally designed by Mikey Dickerson of the United States Digital Service (and– surprise, surprise –Google). The hierarchy says that as you are trying to add reliability to a system, you need to walk through each level before you get to the next one.

The following diagram shows a slightly modified version of Mikey's original pyramid. I have updated it to include the all-encompassing aspect of communication:

Figure 2: This seven-layer pyramid is encircled with communication. Each layer builds upon and needs the previous layer. It is surrounded by communication because each layer needs communication to succeed.

Let us walk through the layers as a preview of what you can expect in each chapter.

One way to use this book is as a framework for working on a new project. As each chapter is about a different level of the hierarchy, you can work through the book to figure out where in the hierarchy your project sits. If it is a new project, then often it will be right at the bottom of the hierarchy, with no, or very little, monitoring implemented.

At each level, if there are others on the team, then you should begin a conversation to figure out what exists, and if it meets the team's needs. Each chapter will provide a rough rubric for that discussion, but remember that every team and project is unique. If you are the only person who is thinking about reliability and infrastructure, then you may end up spending a significant amount of time proposing solutions and pushing the project in a certain direction. Just remember that the point is to improve the reliability of the service, help the business, and improve the user's experience of the service.

You may find yourself distracted by each thing that you could fix. It is highly recommended to document the problems that you see first before diving in. Documenting first can be helpful in a few ways. Diving in is very satisfying, but it also may lead you to skip over requirements or spend too much time on a solution that doesn't work for your business (for example, integrating your system with a monitoring service you can't afford, or building a distributed job scheduler when you could have just used a piece of open source software).

So, when joining a new project, or evaluating a new service, here is a set of steps to follow:

The service you are investigating could be a large project with many pieces of software (a service-oriented architecture (SOA) for example) or a single monolithic application. If you are working on a project with many services, then work through each service one at a time. The downside of this can be that if you want to build a framework that will fit all of the services you are interacting with, you will not know how best to solve the problems and needs of them until after you have done a bunch of research and work. The upside is that you will not be pulled immediately in many directions and will be able to focus on one specific service's problems.

Your time and energy are limited resources and, because of this, you will always need to work with more people than you have time for, so make sure to take it slow. Going slow will mean that things do not get lost in the cracks. You also do not want to burn out before each service has its base few levels of its hierarchy filled up.

Alright! We made it through the introduction. We learned what SRE is at a high level, and we talked about the sorts of problems people in the role tend to focus on. We discussed the structure of the book, and also how to apply that structure to a software project.

In the next chapter, we will be diving into the world of monitoring! Monitoring is the foundation of learning about a system. It is how you record historical data about a system and learn about what is actually going on by analyzing the data you collect. By the end of the chapter, you'll know the basics of instrumenting an application, aggregating that data, storing that data, and displaying it.