System reliability is the probability that a system performs as it is expected to under a set of specified conditions throughout a specified period. Organizations use reliability engineering to help to make products more reliable in a cost-effective way. The key objectives of reliability engineering are to reduce the frequency of failures, identify the causes of failures and correct them, figure out ways of coping with failures when they do occur, and estimate the likely reliability of new designs.

SLAs, SLOs and SLIs are fundamental to site reliability engineering (SRE), but what are they and why are they important for delivering services?

Any engineered system does not guarantee 100% uptime. There are bound to be some unforeseen system failures that cause downtime for the customers or create a poor customer experience. It is, therefore, best practice to take into account a margin for plausible failures. An error budget is this margin of error that the customer is informed about beforehand to secure tolerance during system failure for a decided number of hours.

A Service Level Agreement (SLA) consists of many service commitments. It is an essential part of a contract to outsource software development or software support between two or more parties, specifying the duties and the quality and type of service a company would provide for a fee to a customer.

Starting small and scaling your systems to serve billions of requests per month is never an easy path, so how do you build an infrastructure whilst making the right decisions and compromises for your services? Choosing the right technology stack and ensuring your CI/CD pipeline is reliable are two key steps towards this which we will explore.

Resilience is the capability to recover quickly from difficulties or toughness. It is not about preventing failures, but being able to recover from them quickly. As Amazon’s CTO Werner Vogels famously said ‘everything fails all the time’. It’s a fact of life that failures will inevitably happen but what we can do is build applications that can withstand different kinds of failures. For example, in a data center, hardware is going to fail all the time.

Software reliability is the probability of failure-free operations in a computer program for a specified period of time in a specified environment. It is critical for validation in order to determine characteristics in terms of system performance, functional compatibility, maintenance, competency, installation coverage and process documentation continuance. Software reliability helps you to identify and fix bugs, improve performance, and test features.

Clients expect prompt implementation of changes to their software, and this requirement motivates site reliability engineers to incorporate reliability into applications. The healthy practice of observability and monitoring can improve the reliability and security of software systems. Monitoring is the recording and interpreting data from software systems to keep track of their performance.

Site reliability engineering (SRE) is a set of principles that incorporates aspects of software engineering into IT operations. It takes tasks that would typically have been done manually by operations teams and gives them to engineers to solve using software and automation. This helps to create a bridge between development and operations teams. The concept of SRE was created by Google back in 2003. Since then, it has been adopted by thousands of organizations all over the world.

Technical debt is the implied cost of the additional work that is required when a team chooses a quick, easy solution that is limited, instead of a more well-thought-out, higher-quality solution that would take longer. Essentially, it’s what happens when teams prioritize speed over quality. Examples of technical debt include untested code, unreadable code, dead code, duplicated code, or outdated documentation.