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GitOps

GitOps streamlines the deployment process by unifying development and operations under a single version-controlled system.

GitOps is a approach to automating infrastructure and application management using Git as a single source of truth. It leverages the principles of Git-based workflows to control and manage infrastructure and configuration deployments in a declarative manner. This process combines the best practices of DevOps, continuous integration (CI), and continuous delivery (CD), allowing for consistent and reliable infrastructure changes.

1. Concepts and Features

• Declarative

  A system managed by GitOps must have its desired state expressed declaratively.

  The desired state of the system is defined using declarative infrastructure and configuration files.

• Versioned and Immutable

  Desired state is stored in a way that enforces immutability, versioning and retains a complete version history.

• Pulled Automatically

  Software agents automatically pull the desired state declarations from the source.

Software agents or controllers monitor the Git repository for changes and synchronize the live environment with the desired state defined in Git.

• Continuously Reconciled

  Software agents continuously observe actual system state and attempt to apply the desired state.

Terminology

• Continuous

  Continuous is intended to match the industry standard term: reconciliation continues to happen, not that it must be instantaneous.

• Declarative Description

  A configuration that describes the desired operating state of a system without specifying procedures for how that state will be achieved. This separates configuration (the desired state) from the implementation (commands, API calls, scripts etc.) used to achieve that state.

• Desired State

  The aggregate of all configuration data that is sufficient to recreate the system so that instances of the system are behaviourally indistinguishable. This configuration data generally does not include persistent application data, eg. database contents, though often does include credentials for accessing that data, or configuration for data recovery tools running on that system.

• Drift

  When a system's actual state has moved or is in the process of moving away from the desired state, this is often referred to as drift.

• Pull

  Pulled Automatically specifies the desired state must be pulled rather than pushed, primarily because the software agents must be able to access the desired state from the state store at any time, not only when there is an intentional change in the state store triggering a push event. This is a prerequisite for reconciliation to happen continuously, as specified in principle 4 (Continuously Reconciled). Note that – in contrast to traditional CI/CD, where automation is generally driven by pre-set triggers – in GitOps, reconciliation is triggered whenever there is a divergence. Divergence could be due to the actual state unintentionally drifting from the desired state declarations – not only due to a new desired state declaration version having been changed intentionally.

• Reconciliation

  The process of ensuring the actual state of a system matches its desired state. Contrary to traditional CI/CD where automation is generally driven by pre-set triggers, in GitOps reconciliation is triggered whenever there is a divergence. Divergence could be due to the actual state unintentionally drifting from the desired state declarations, or a new desired state declaration version having been changed intentionally. Actions are taken based on policies around feedback from the system and previous reconciliation attempts, in order to reduce deviation over time.

• Software System

  A software system managed by GitOps includes:

  1. One or more runtime environments consisting of resources under management
  2. The management agents within each runtime
  3. Policies for controlling access and management of repositories, deployments, runtimes

• State Store

  A system for storing immutable versions of desired state declarations. This state store should provide access control and auditing on the changes to the Desired State. Git, from which GitOps derives its name, is the canonical example used as this state store but any other system that meets these criteria may be used. In all cases, these state stores must be properly configured and precautions must be taken to comply with requirements set out in the GitOps Principles.

• Feedback

  Open GitOps follows control-theory and operates in a closed-loop. In control theory, feedback represents how previous attempts to apply a desired state have affected the actual state. For example if the desired state requires more resources than exist in a system, the software agent may make attempts to add resources, to automatically rollback to a previous version, or to send alerts to human operators.

References

• GitHub Open GitOps repository.