RST Software
Editorial Team
Ross Krawczyk
Reviewed by a tech expert

What is SRE? – Understanding Site Reliability Engineering

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Have you ever wondered how Google keeps its numerous services up and running smoothly, handling billions of requests each day without interruptions? The secret lies in an innovative approach called Site Reliability Engineering (SRE) that enables them to “automate away” reliability risks at scale. In this comprehensive guide, we will unravel the mysteries of Site Reliability Engineering – its origins, principles, tools and best practices – to help you assess if adopting SRE could transform reliability for your company.

What is Site Reliability Engineering (SRE)

Site Reliability Engineering is a discipline that combines software and systems engineering to build and efficiently run large-scale distributed systems.

SRE was pioneered by Google in 2003 to solve crucial problems around managing complex systems at scale. Today, it has evolved into a mature, codified set of practices that enable Google to consistently deliver highly reliable services like Gmail, Search and YouTube to billions of users.

As Google’s VP of Engineering, once Site Reliability Engineer, Ben Treynor Sloss puts it: “SRE is what happens when you ask a software engineer to design an operations function.” This includes:

  • comprehensive automation,
  • proactive prevention of outages, and
  • world-class incident response when outages do occur.

At its core, Site Reliability Engineering brings the rigors of software engineering to IT operations – treating “ops” work as software problems to solve.

Importance of SRE in modern software development

Site Reliability Engineering has become essential for any organization running large, complex services and applications, for several reasons:

1. Software now runs the world. Software – the invisible bits behind our shiny device interfaces – has become the brains behind delivering modern digital services. As software eats the world, the scale and complexity of these services are exploding exponentially.

2. Reliability is crucial. For any revenue-critical online service, downtime directly impacts revenue and reputation. Users expect 100% uptime and performance. Even brief outages or latency spikes cause lost business and frustrated customers.

3. Complexity is the enemy of reliability. Modern distributed systems comprising endless chains of interconnected microservices are inherently unstable. More complexity means more opportunities for something to break badly.

4. Manual operations do not scale. Humans are simply unable to handle the complexity manually at scale. When overstretched Ops teams frantically fight fires, reliability suffers.

Site Reliability Engineering injects software engineering rigour into service operations to address these realities. SREs design automated systems that detect and fix problems in seconds, long before users are impacted. This is the only sustainable way to maintain reliability at scale.

As Google's services grow exponentially in usage, SRE's “automation first” approach has been crucial for keeping services stable and available. Without Site Reliability Engineering, Google could not have reached its current state.

Key challenges that SRE aims to address

SRE was created to solve two fundamental challenges in running complex, distributed systems at scale:

  • The tension between agility and reliability – software engineering teams strive to release new code quickly to add features and respond to user needs. But frequent updates risk destabilizing a service and causing outages.
  • The toil of manual operations – mundane upkeep tasks like server reboots do not scale; humans cannot keep up. SRE replaces repetitive manual work with automated self-healing systems. This increases operational scale while reducing costs and human toil.

By addressing these core tensions, SRE enables delivering new value quickly without compromising reliability.

Core principles of SRE

Working closely with development and operation teams, site reliability engineers follow several key principles and practices for running resilient, scalable services:

  • Measure quality of service – use Service Level Objectives (SLOs), Indicators (SLIs) and Agreements (SLAs) to have control at everything that matters for providing high quality services.
  • Accept failures and errors as normal part of the process – employ SRE's error budget principle, which balances the pace of innovation and system stability.
  • Leverage automation – automate as many repetitive and IT infrastructure tasks as possible, ideally to make your system maintenance-free.

Measuring quality of service

Measuring the quality of service provided by an organization is one of the most important units of SRE. There are three interconnected terms that form the basis of understanding the concept of service level in Site Reliability Engineering:

  • Service Level Objectives (SLOs) – serve as a benchmark for indicators, parameters, or metrics defined with specific service level targets. Selecting Service Level Objectives is not solely a technical task, as the choices made have implications for both the product and the business. The objectives may be an optimal range or a specific value for each service function or process that constitutes a cloud service. They are typically expressed as a percentage over a period of time, and define target thresholds for SLIs.
  • Service Level Indicators (SLIs) – are metrics like request latency and error rates. In other words, Service Level Indicator is a specific metric that helps an organization to measure certain aspects of the level of services to their customers. They are usually measured as percentages, with 100% being perfect performance. SLIs are a subsection of Service Level Objectives (SLOs), which are in turn part of Service Level Agreements (SLAs).
  • Service Level Agreements (SLAs) – are contracts between a service provider and a customer, defining the types and standards of services to be offered. In other words, SLAs contractualize SLOs for paying customers. The most common component of an SLA is that the services should be provided to the customer as agreed upon in the contract.

Handling error budget in SRE

Derived from the Service Level Objective (SLO), which specifies the expected uptime or performance level of a service, an error budget is a quantifiable metric that sets the allowable level of unreliability for a service within a specific timeframe, usually a quarter. The idea is simple: calculate the difference between the expected and actual uptime, and you get your “error budget”, the amount of “unreliability” you can afford.

The error budget serves as a common ground for SRE engineers and product development teams. When there is remaining error budget, it indicates that the system is performing well, and new features can be released. If the error budget gets depleted due to outages or other issues, it's a signal to slow down and focus on improving system reliability before rolling out anything new.

For example, if your SLO has a 99.999% success rate for all queries during a quarter, and you only fail 0.0002%, then you have used up 20% of your error budget. If you exceed the budget, no new features are rolled out until the system is stabilized.

The error budget helps maintain a balance between system reliability and the pace of innovation. When the error budget is high, teams can take more risks. When it is low, caution is exercised.

Leverage automation in SRE

Any time a human operator has to manually interact with a system during regular operations, it is considered a flaw. This is where the automation principle comes in for SRE engineering. By systematically automating routine, repetitive, and manual tasks, you can minimize human error, reduce the operational burden, and allow engineers to focus more on creating long-term value. The intent is to make your IT infrastructure and operations as maintenance-free as possible.

The importance of automation in SRE cannot be overstated. It serves as a multiplicative force for the team's productivity, allowing for a scalable approach to managing increasingly complex systems. Automation enables SRE teams to move fast without compromising the reliability and performance of the services they manage. It also aligns with the principle of reducing human toil, a goal explicitly targeted to be less than 50% of each SRE's time, allowing them to engage in more proactive, strategic engineering work.

SRE vs. DevOps – what’s the difference?

SRE and DevOps share philosophies of automating operations and improving collaboration between developers and operations teams. But there are key differences:

  • Focus – Site Reliability Engineering focuses on availability, latency, and performance. DevOps focuses on faster delivery of new code.
  • Objectives – SRE optimizes for reducing disruptions from changes. DevOps optimizes for increasing rate of deployment.
  • Metrics – Site Reliability Engineering measures Service Level Objectives (SLOs) and Service Level Indicators (SLIs) for reliability. DevOps measures deployment velocity and lead time.
  • Evolution – SRE evolved from Ops experience. DevOps evolved from Agile software development practices.

SRE vs DevOps is not a duel of opposites. They are complementary disciplines with different centers of gravity, and many organizations practice them together, with SRE providing guardrails around reliability risks.

The SRE toolkit

Incident management is pivotal in Site Reliability Engineering toolkit, focused on minimizing service interruptions and quickly resuming business activities. Unlike traditional approaches, SRE emphasizes managing incidents proactively, adjusting the system to automatically respond to incidents, and self-heal. This involves chaos testing, such as intentionally shutting down servers to assess system resilience and response procedures.

Before testing, it is crucial to study past incidents and blameless postmortems to identify key metrics. These insights inform the configuration of monitoring tools and alerting rules, which are executed through specialized SRE software.

  1. Prometheus – time-series monitoring systems like Prometheus track service metrics like latency, traffic, and errors. Monitoring provides vital observability into system state. Prometheus excels in collecting and processing numeric time-series data. It gathers, organizes, and stores metrics along with unique identifiers and timestamps, and implements a highly dimensional data model where time series are identified by a metric name and a set of key-value pairs. It allows slicing and dicing of collected time series data in order to generate ad-hoc graphs, tables, and alerts.
  2. Grafana – open-source operational dashboards for running data analytics, visualization, and pulling up metrics that make sense of the massive amount of data and to monitor apps with the help of customizable dashboards. Grafana offers plugins, dashboards, alerts, and different user-level access for governance as an observability tool. It also provides fine-grained actions to manipulate Kubernetes resources.
  3. Kubernetes – stands out in automating deployment, scaling, and management of containerized applications. This open-source platform groups containers that make up an application into logical units for easy management and discovery. Some of the open-source Kubernetes tools for SRE and Ops teams include Kube-ops-view, Cabin, Kubectx, and Kube-shell among others. These tools provide operational views for multiple Kubernetes clusters, allow switching between clusters and namespaces when using kubectl, provide integrated shells for working with the Kubernetes CLI, and more.
» Practical guidelines for using Kubernetes on AWS EKS «

How to implement SRE in your company

Making the shift from traditional Ops to SRE is challenging, but worthwhile for teams running crucial digital services. Hiring a Site Reliability Engineer is a tempting option, however, it is not necessary to prepare your organization to work in compliance with SRE framework. Here are tips:

  • Start small – introduce SRE principles incrementally in problematic areas like incident response. Do not boil the ocean.
  • Focus on automation – automating repetitive manual work should be the north star. This increases scalability and frees up engineering time.
  • Instrument everything – monitoring based on time-series data and metrics is the bedrock for automation and self-healing.
  • Standardize Site Reliability Engineering metrics – align objectives around availability and system quality between developers, product and SRE.
  • Hire software engineers – SREs need solid software engineering skills to build automation and tooling. Ops experience is helpful but not required.
  • Use error budgets – establish error budgets between product and SRE to balance innovation and reliability, rather than forcing 100% uptime.

Best practices for implementing SRE

When making the transition into Site Reliability Engineering, apply proven best practices to make it smooth and effective:

  • Instrument applications early to start generating time-series monitoring data. This unlocks automation opportunities.
  • Introduce postmortems early to foster learning from failures, before blame culture becomes entrenched.
  • Start chaos testing in non-production environments, and gradually increase realism and blast radius.
  • Establish error budgets and SLIs/SLOs incrementally for each service. Automate manual tasks one by one. Target repetitive, high-value tasks first.
  • Rotate team members through all SRE roles like on-call to cross-train and retain operational knowledge.
  • Evangelize SRE's benefits to stakeholders using error budgets, postmortems and empirical reliability data.
  • Celebrate and reward behaviors like thorough postmortems, effective incident response and toil reduction.

Adopting these practices methodically, rather than attempting to “be Google”, will set any team up for a successful SRE transformation.

The future of SRE

The strategic importance of Site Reliability Engineering is likely to escalate as services grow at scale and become increasingly complex. Several key emerging trends are rooted in the integration of artificial intelligence:

  • AI for automated incident response – AI can analyze historical and real-time data to detect, diagnose, and resolve incidents faster and more effectively. It can also suggest or implement appropriate remediation actions, reducing the human intervention and error.
  • Intelligent load balancing – traffic patterns and system utilization can be tracked by artificial intelligence to dynamically adjust load balancers to optimize resource allocation and prevent overloads. This can improve the system performance and user experience, especially during peak times or unexpected surges.
  • Refining and defining SLIs, SLOs and SLAs – AI analytics can aid in the fine-tuning of Service Level Indicators, Objectives, and Agreements by providing data-driven insights into system behavior and customer experience, making them more aligned and realistic.
  • NoOps – artificial intelligence paves the way for a fully automated IT environment. Serverless and autoscaling infrastructure can gradually eliminate traditional ops toil, freeing engineers to focus on crafting specialized automation and fine-tuning SRE practices.
  • Self-healing systems – AI can enable systems to self-diagnose and self-heal in response to common issues, such as configuration errors, resource exhaustion, or network failures. It can also learn from previous incidents and apply preventive measures to avoid recurrence. This can improve the system resilience and availability.

As these trends progress, SRE skills and culture will become ubiquitous among successful engineering teams. Just as Google SRE has been crucial for handling Google's scale, SRE will soon be crucial for any company building complex software services that users depend on.

How can RST help you adopt SRE principles?

Implementing SRE can transform system reliability, availability and scalability, but requires adopting fundamentally new operating paradigms tailored for today's software-centric world. While it takes commitment and cultural change, the payoff is worth the effort for teams operating complex mission-critical services.

Want to start applying SRE principles like blameless postmortems and error budgeting to make your services more resilient? Check out the SRE books for detailed case studies:

And contact us if you need with adopting SRE principles within your organization.

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