What Is GitOps?
Learn what GitOps is, GitOps goals and ideals, limitations, tools that support GitOps, and the practical implications of adopting GitOps in your own organization.
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GitOps is a relatively new addition to the growing list of "Ops" paradigms taking shape in our industry. It all started with DevOps, and while the term DevOps has been around for some years now, it seems we still can't agree whether it's a process, mindset, job title, set of tools, or some combination of them all. We captured our thoughts about DevOps in our introduction to DevOps post, and we dive even deeper in our DevOps engineer's handbook.
The term GitOps suffers from the same ambiguity, so in this post we look at:
- The history of GitOps
- GitOps goals and ideals
- The limitations of GitOps
- The tools that support GitOps
- The practical implications of adopting GitOps in your own organization
The term GitOps was originally coined in a blog post by WeaveWorks called GitOps - Operations by Pull Request. The post described how WeaveWorks used Git as a source of truth, leading to the following benefits:
Since that original blog post, initiatives like the GitOps Working Group have been organized to:
This working group recently released version one of their principles, which states that:
The contrast between low level implementations of GitOps found in most blog posts and the high level ideals of a GitOps system described by the working group is worth discussion, as the differences between them is a source of much confusion.
GitOps Doesn't Imply the Use of Git
Most discussions around GitOps center on how building processes on Git give rise to many of the benefits ascribed to the GitOps paradigm. Git naturally provides an (almost) immutable history of changes, with changes annotated and approved via pull requests, and where the current state of the Git repository naturally represents the desired state of a system, thus acting as a source of truth. The overlap between Git and GitOps is undeniable.
However, you may have noticed that Git was never mentioned as a requirement of GitOps by the working group. So while Git is a convenient component of a GitOps solution, GitOps itself is concerned with the functional requirements of a system rather than checking your declarative templates into Git.
This distinction is important, because many teams fixate on the "Git" part of GitOps. The term GitOps is an unfortunate name for the concept it's trying to convey, leading many to believe Git is the central aspect of GitOps. But GitOps has won the marketing battle and gained mind share in IT departments. While it may be a restrictive term to describe functional requirements unrelated to Git, GitOps is now the shorthand for describing processes that implement a set of high level concerns.
Kubernetes was the first widely used platform to combine the ideas of declarative state and continuous reconciliation with an execution environment to implement the reconciliation and host running applications. It really is magic to watch a Kubernetes cluster reconfigure itself to match the latest templates applied to the system. So it's no surprise that Kubernetes is the foundation of GitOps tools like Flux and Argo CD, while posts like 30+ Tools List for GitOps mention Kubernetes 20 times.
While continuous reconciliation is impressive, it's not really magic. Behind the scenes Kubernetes runs a number of operators that are notified of configuration changes and execute custom logic to bring the cluster back to the desired state.
The key requirements of continuous reconciliation are:
- Access to the configuration or templates declaratively expressing the desired state
- The ability to execute a process capable of reconciling a system when configuration is changed
- An environment in which the process can run
Kubernetes bakes these requirements into the platform, making it easy to achieve continuous reconciliation. But these requirements can also be met with some simple orchestration, Infrastructure as Code (IaC) tools like Terraform, Ansible, Puppet, Chef, CloudFormation, Arm Templates, and an execution environment like a CI server:
- IaC templates can be stored in Git, file hosting platforms like S3 or Azure Blob Storage, complete with immutable audit histories.
- CI/CD systems can poll the storage, are notified of changes via webhooks, or have builds or deployments triggered via platforms like GitHub Actions.
- The IaC tooling is then executed, bringing the system in line with the desired state.
Indeed, a real world end-to-end GitOps system inevitably incorporates orchestration outside of Kubernetes. For example, Kubernetes is unlikely to manage your DNS records, centralized authentication platforms, or messaging systems like Slack. You'll also likely find at least one managed service for things like databases, message queues, scheduling, and reporting more compelling than attempting to replicate them in a Kubernetes cluster. Also, any established IT department is guaranteed to have non-Kubernetes systems that would benefit from GitOps.
So while the initial selection of specialized GitOps tools tends to be tightly integrated into Kubernetes, achieving the functional requirements of GitOps across established infrastructure will inevitably require orchestrating one or more IaC tools.
Continuous reconciliation, as described by the working group, describes responses to two types of system changes.
The first is what you expect, where deliberate changes to the configuration held in Git or other versioned storage is detected and applied to the system. This is the logical flow of configuration change and represents the normal operation of a correctly configured GitOps workflow.
The second is where an agent detects undesirable changes to the system that are not described in the source configuration. In this case, your system no longer reflects the desired state, and the agent is expected to reconcile the system back to the configuration maintained in Git.
This ability to resolve the second situation is a neat technical capability, but represents an incomplete business process.
Imagine the security guards from your front desk reporting they had evicted an intruder. As a once-off occurrence, this report would be mildly concerning, but the security team did their job and resolved the issue. But now imagine you were receiving these reports every week. Obviously there is a more significant problem forcing the security team to respond to weekly intrusions.
In the same manner, a system that continually removes undesirable system states is an incomplete solution to a more fundamental root problem. The real question is who is making those changes, why are the changes being made, and why are they not being made through the correct process?
The fact your system can respond to undesirable states is evidence of a robust process able to adapt to unpredictable events, and this ability should not be underestimated. It's a long established best practice that teams should exercise their recovery processes, so in the event of disaster, teams are able to run through a well-rehearsed restoration. Continuous reconciliation can be viewed as a kind of automated restoration process, allowing the process to be tested and verified with ease.
But if your system has to respond to undesirable states, it's evidence of a flawed process where people have access that they shouldn't or are not following established processes. An over-reliance on a system that can undo undesirable changes after they've been made runs the risk of masking a more significant underlying problem.
While GitOps describes many desirable traits of well-managed infrastructure and deployment processes, it's not a complete solution. In addition to the 4 functional requirements described by GitOps, a robust system must be:
- Verifiable - infrastructure and applications must be testable once they are deployed.
- Recoverable - teams must be able to recover from an undesirable state.
- Visible - the state of the infrastructure and the applications deployed to it must be surfaced in an easily consumed summary.
- Secure - rules must exist around who can make what changes to which systems.
- Measurable - meaningful metrics must be collected and exposed in an easily consumed format.
- Standardized - applications and infrastructure must be described in a consistent manner.
- Maintainable - support teams must be able to query and interact with the system, often in non-declarative ways.
- Coordinated - changes to applications and infrastructure must be coordinated between teams.
GitOps offers little advice or insight into what happens before configuration is committed to a Git repo or other versioned and immutable storage, but it is "left of the repo" where the bulk of your engineering process will be defined.
If your Git repo is the authoritative representation of your system, then anyone who can edit a repo essentially has administrative rights. However, Git repos don't provide a natural security boundary for the kind of nuanced segregation of responsibility you find in established infrastructure. This means you end up creating one repo per app per environment per role. Gaining visibility over each of these repos and ensuring they have the correct permissions is no trivial undertaking.
You also quickly find that just because you can save anything in Git doesn't mean you should. It's not hard to imagine a rule that says development teams must create Kubernetes deployment resources instead of individual pods, use ingress rules that respond to very specific hostnames, and always include a standard security policy. This kind of standardization is tedious to enforce through pull requests, so a much better solution is to give teams standard resource templates that they populate with their specific configuration. But this is not a feature inherent to Git or GitOps.
We then have those processes "right of the cluster," where management and support tasks are defined.
Reporting on the intent of a Git commit is almost impossible. If you looked at a diff between two commits and saw that a deployment image tag was increased, new secret values were added, and a config map was deleted, how would you describe the intent of that change? The easy answer is to read the commit message, but this isn't a viable option for reporting tools that must map high level events like "deployed a new app version" or "bug fix release" (which are critical if you want to measure yourself against standard metrics like those presented in the DORA report) to the diff between two commits. Even if you could divine an algorithm that understood the intent of a Git commit, a Git repo was never meant to be used as a time-series database.
GitOps also provides no guidance on how to perform support tasks after the system is in its desired state. What would you commit to a Git repo to delete misbehaving pods so they can be recreated by their parent deployment? Maybe a job could do this, but you have to be careful that Kubernetes doesn't try to apply that job resource twice. But then what would you commit to the repo to view the pod logs of a service like an ingress controller that was preinstalled on your cluster? My mind boggles at the thought of all the asynchronous message handling you would need to implement to recreate
kubectl logs mypod in a GitOps model.
Adhoc reporting and management tasks like this don't have a natural solution in the GitOps model.
This is not to say that GitOps is flawed or incomplete, but rather that it solves specific problems, and must be complemented with other processes and tools to satisfy basic operational requirements.
I'd like to present you with a theory and a thought experiment to apply it to:
In any sufficiently complex GitOps process, your Git repo is just another structured database.
You start your GitOps journey using the common combination of Git and Kubernetes. All changes are reviewed by pull request, committed to a Git repo, consumed by a tool like Argo CD or Flux, and deployed to your cluster. You have satisfied all the functional requirements of GitOps, and enjoy the benefits of a single source of truth, immutable change history, and continuous reconciliation.
But it becomes tedious to have a person open a pull request to bump the image property in a deployment resource every time a new image is published. So you instruct your build server to pull the Git repo, edit the deployment resource YAML file, and commit the changes. You now have GitOps and CI/CD.
You now need to measure the performance of your engineering teams. How often are new releases deployed to production? You quickly realize that extracting this information from Git commits is inefficient at best, and that the Kubernetes API was not designed for frequent and complex queries, so you choose to populate a more appropriate database with deployment events.
As the complexity of your cluster grows, you find you need to implement standards regarding what kind of resources can be deployed. Engineering teams can only create deployments, secrets, and configmaps. The deployment resources must include resource limits, a set of standard labels, and the pods must not be privileged. In fact, it turns out that of the hundreds of lines of YAML that make up the resources deployed to the cluster, only about 10 should be customized. As you did with the image tag updates, you lift the editing of resources from manual Git commits to an automated process where templates have a strictly controlled subset of properties updated with each deployment.
Now that your CI/CD is doing most of the commits to Git, you realize that you no longer need to use Git repos as a means of enforcing security rules. You consolidate the dozens of repos that were created to represent individual applications and environments to a single repo that only the CI/CD system interacts with on a day-to-day basis.
You find yourself having to roll back a failed deployment, only to find that the notion of reverting a Git commit is too simplistic. The changes to the one application you wanted to revert have been mixed in with a dozen other deployments. Not that anyone should be touching the Git repo directly anyway, because merge conflicts can have catastrophic consequences. But you can use your CI/CD server to redeploy an old version of the application, and because the CI/CD server has the context of what makes up a single application, the redeployment only changes the files relating to that application.
At this point, you concede that your Git repo is another structured database reflecting a subset of "the source of truth:"
- Humans aren't to touch it.
- All changes are made by automated tools.
- The automated tools require known files of specific formats in specific locations.
- The Git history shows a list of changes made by bots rather than people.
- The Git history now reads "Deployment #X.Y.Z", and other commit information only makes sense in the context of the automated tooling.
- Pull requests are no longer used.
- The "source of truth" is now found in the Git repo (showing changes to files), the CI/CD platform's history (showing the people who initiated the changes, and the scripts that made them), and the metrics database.
- You consolidated your Git repos, meaning you have limited ability to segregate access to humans even if you want to.
You also realize that the parts of your GitOps process that are adding unique business value are "left of the repo" with metrics collection, standardized templates, release orchestration, rollbacks, and deployment automation; and "right of the cluster" with reports, dashboards, and support scripts. The process between the Git repo and cluster is now so automated and reliable that it's not something you need to think about.
GitOps has come to encapsulate a subset of desirable functional requirements that are likely to provide a great deal of benefit for any teams that fulfill them. While neither Git nor Kubernetes are required to satisfy GitOps, they are the logical platforms on which to start your GitOps journey, as they're well supported by the more mature GitOps tools available today.
But GitOps tooling tends to be heavily focused on what happens between a commit to a Git repo and the Kubernetes cluster. While this is no doubt a critical component of any deployment pipeline, there's much work to be done "left of the repo" and "right of the cluster" to implement a robust CI/CD pipeline and DevOps workflow.
GitOps tools also tend to assume that because everything is in Git, the intent of every change is annotated with commit messages, associated with the author, put through a review process, and is available for future inspection. However, this is overly simplistic, as any team advanced enough to consider implementing GitOps will immediately begin iterating on the process by automating manual touch points, usually with respect to how configuration is added to the Git repo in the first place.
As you project the natural evolution of a GitOps workflow, you're likely to conclude that so many automated processes rely on the declarative configuration being in a specific location and format, that Git commits must be treated in much the same way as a database migration. The inputs to a GitOps process must be managed and orchestrated, and the outputs must be tested, measured, and maintained. Meanwhile the processing between the Git repo and cluster should be automated, rendering much of what we talk about as GitOps today as simply an intermediate step in a specialized CI/CD pipeline or DevOps workflow.
Perhaps the biggest source of confusion around GitOps is the misconception that it represents an end-to-end solution, and that you implement GitOps and GitOps-focused tooling to the exclusion of alternative processes and platforms.
In practice, GitOps encapsulates one step in your infrastructure and deployment pipelines, and must be complemented with other processes and platforms to fulfill common business requirements.
Published at DZone with permission of Matthew Casperson. See the original article here.
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