Agile: Set of principles for software development lifecycle that promotes small, manageable changes quickly, ongoing collaboration, early delivery of working software, and continuous improvement in support of a business mission.
DevOps: Practice and culture shift driving Software Engineering (SE) and Production Management (PM) to collaborate together throughout the delivery lifecycle. Emphasis on shifting stability and security to the left with automation throughout the delivery pipeline. Ideally integrates with Agile practices to define feature success and prioritize the work with both teams present.
Site Reliability Engineering (SRE): Practice supported by skilled engineers, to establish and adhere to availability targets, service level objectives (SLOs), and error budgets set by end users. SREs have the ability to modify code to ensure adherence, and have basic telemetry capability to monitor where and when to modify applications.
SRE x DevOps Comparison
DevOps Primary Focus = Delivery Speed
DevOps is a set of principles and practices that aims to break down IT silos and encourage collaboration, continuous delivery and delivery automation, Infrastructure as Code and joint (or even collapsed) responsibility for development and operate teams.
SRE Primary Focus = Reliability
SRE is a job function, where engineers are empowered to improve the reliability of a of a system by developing advanced telemetry, defining acceptable service levels and enforcing error budgets by accepting or rejecting code releases.
DEV SRE
DevOPS and SRE
Set of processes, practices, tools, standards, patterns, people, culture