Does Argo Rollouts depend on Argo CD or any other Argo project?¶
Argo Rollouts is a standalone project. Even though it works great with Argo CD and other Argo projects, it can be used on its own for Progressive Delivery scenarios. More specifically, Argo Rollouts does NOT require that you also have installed Argo CD on the same cluster.
How does Argo Rollouts integrate with Argo CD?¶
Argo CD understands the health of Argo Rollouts resources via Argo CD’s Lua health check. These Health checks understand when the Argo Rollout objects are Progressing, Suspended, Degraded, or Healthy. Additionally, Argo CD has Lua based Resource Actions that can mutate an Argo Rollouts resource (i.e. unpause a Rollout).
As a result, an operator can build automation to react to the states of the Argo Rollouts resources. For example, if a Rollout created by Argo CD is paused, Argo CD detects that and marks the Application as suspended. Once the new version is verified to be good, the operator can use Argo CD’s resume resource action to unpause the Rollout so it can continue to make progress.
Can we run the Argo Rollouts kubectl plugin commands via Argo CD?¶
Argo CD supports running Lua scripts to modify resource kinds (i.e. suspending a CronJob by setting the
.spec.suspend to true). These Lua Scripts can be configured in the argocd-cm ConfigMap or upstreamed to the Argo CD's resource_customizations directory. These custom actions have two Lua scripts: one to modify the said resource and another to detect if the action can be executed (i.e. A user should not be able to resuming a unpaused Rollout). Argo CD allows users to execute these actions via the UI or CLI.
In the CLI, a user (or a CI system) can run
argocd app actions run <APP_NAME> <ACTION>
In the UI, a user can click the hamburger button of a resource and the available actions will appear in a couple of seconds. The user can click and confirm that action to execute it.
Currently, the Rollout action has two available custom actions in Argo CD: resume and restart.
- Resume unpauses a Rollout with a PauseCondition
- Restart: Sets the RestartAt and causes all the pods to be restarted.
Does Argo Rollout require a Service Mesh like Istio?¶
Argo Rollouts does not require a service mesh or ingress controller to be used. In the absence of a traffic routing provider, Argo Rollouts manages the replica counts of the canary/stable ReplicaSets to achieve the desired canary weights. Normal Kubernetes Service routing (via kube-proxy) is used to split traffic between the ReplicaSets.
Does Argo Rollout require we follow GitOps in my organization?¶
Argo Rollouts is a Kubernetes controller that will react to any manifest change regardless of how the manifest was changed. The manifest can be changed
by a Git commit, an API call, another controller or even a manual
kubectl command. You can use Argo Rollouts with any traditional CI/CD
solution that does not follow the GitOps approach.
Can we run the Argo Rollouts controller in HA mode?¶
Yes. A k8s cluster can run multiple replicas of Argo-rollouts controllers to achieve HA. To enable this feature, run the controller with
--leader-elect flag and increase the number of replicas in the controller's deployment manifest. The implementation is based on the k8s client-go's leaderelection package. This implementation is tolerant to arbitrary clock skew among replicas. The level of tolerance to skew rate can be configured by setting
--leader-election-renew-deadline appropriately. Please refer to the package documentation for details.
Which deployment strategies does Argo Rollouts support?¶
Argo Rollouts supports BlueGreen, Canary, and Rolling Update. Additionally, Progressive Delivery features can be enabled on top of the blue-green/canary update, which further provides advanced deployment such as automated analysis and rollback.
Does the Rollout object follow the provided strategy when it is first created?¶
As with Deployments, Rollouts does not follow the strategy parameters on the initial deploy. The controller tries to get the Rollout into a steady state as fast as possible by creating a fully scaled up ReplicaSet from the provided
.spec.template. Once the Rollout has a stable ReplicaSet to transition from, the controller starts using the provided strategy to transition the previous ReplicaSet to the desired ReplicaSet.
How does BlueGreen rollback work?¶
A BlueGreen Rollout keeps the old ReplicaSet up and running for 30 seconds or the value of the scaleDownDelaySeconds. The controller tracks the remaining time before scaling down by adding an annotation called
argo-rollouts.argoproj.io/scale-down-deadline to the old ReplicaSet. If the user applies the old Rollout manifest before the old ReplicaSet scales down, the controller does something called a fast rollback. The controller immediately switches the active service’s selector back to the old ReplicaSet’s rollout-pod-template-hash and removes the scaled down annotation from that ReplicaSet. The controller does not do any of the normal operations when trying to introduce a new version since it is trying to revert as fast as possible. A non-fast-track rollback occurs when the scale down annotation has past and the old ReplicaSet has been scaled down. In this case, the Rollout treats the ReplicaSet like any other new ReplicaSet and follows the usual procedure for deploying a new ReplicaSet.
What is the
Argo Rollouts adds an
argo-rollouts.argoproj.io/managed-by-rollouts annotation to Services and Ingresses that the controller modifies. They are used when the Rollout managing these resources is deleted and the controller tries to revert them back into their previous state.
Does Argo Rollouts write back in Git when a rollback takes place?¶
No. Argo Rollouts doesn't read/write anything to Git. Actually Argo Rollouts knows nothing about Git repositories (only Argo CD has this information if it manages the Rollout). When a rollback takes place, Argo Rollouts marks the application as "degraded" and changes the version on the cluster back to the known stable one.
If I use both Argo Rollouts and Argo CD wouldn't I have an endless loop in the case of a Rollback?¶
No there is no endless loop. As explained already in the previous question, Argo Rollouts doesn't tamper with Git in any way. If you use both Argo projects together, the sequence of events for a rollback is the following:
- Version N runs on the cluster as a Rollout (managed by Argo CD). The Git repository is updated with version N+1 in the Rollout/Deployment manifest
- Argo CD sees the changes in Git and updates the live state in the cluster with the new Rollout object
- Argo Rollouts takes over as it watches for all changes in Rollout Objects. Argo Rollouts is completely oblivious to what is happening in Git. It only cares about what is happening with Rollout objects that are live in the cluster.
- Argo Rollouts tries to apply version N+1 with the selected strategy (e.g. blue/green)
- Version N+1 fails to deploy for some reason
- Argo Rollouts scales back again (or switches traffic back) to version N in the cluster. No change in Git takes place from Argo Rollouts
- Cluster is running version N and is completely healthy
- The Rollout is marked as "Degraded" both in ArgoCD and Argo Rollouts.
- Argo CD syncs take no further action as the Rollout object in Git is exactly the same as in the cluster. They both mention version N+1
So how can I make Argo Rollouts write back in Git when a rollback takes place?¶
You don't need to do that if you simply want to go back to the previous version using Argo CD. When a deployment fails, Argo Rollouts automatically sets the cluster back to the stable/previous version as explained in the previous question. You don't need to write anything in Git to achieve this. The cluster is still healthy and you have avoided downtime. You are then expected to fix the issue and roll-forward (i.e. deploy the next version) if you want to follow GitOps in a pedantic manner. If you want Argo Rollouts to write back in Git after a failed deployment then you need to orchestrate this with an external system or write custom glue code. But this is normally not needed.
What is the relationship between Rollbacks with Argo Rollouts and Rollbacks with Argo CD?¶
They are completely unrelated. Argo Rollouts "rollbacks" switch the cluster back to the previous version as explained in the previous question. They don't touch or affect Git in any way. Argo CD rollbacks simply point the cluster back a previous Git hash. Normally if you have Argo Rollouts, you don't need to use the Argo CD rollback command.
How can I deploy multiple services in a single step and roll them back according to their dependencies?¶
The Rollout specification focuses on a single application/deployment. Argo Rollouts knows nothing about application dependencies. If you want to deploy multiple applications together in a smart way (e.g. automatically rollback a frontend if backend deployment fails) you need to write your own solution on top of Argo Rollouts. In most cases, you would need one Rollout resource for each application that you are deploying. Ideally you should also make your services backwards and forwards compatible (i.e. frontend should be able to work with both backend-preview and backend-active).
How can I run my own custom tests (e.g. smoke tests) to decide if a Rollback should take place or not?¶
Use a custom Job or Web Analysis. You can pack all your smoke tests in a single container and run them as a Job analysis. Argo Rollouts will use the results of the analysis to automatically rollback if the tests fail.
Why doesn't my Experiment end?¶
An Experiment’s duration is controlled by the
.spec.duration field and the analyses created for the Experiment. The
.spec.duration indicates how long the ReplicaSets created by the Experiment should run. Once the duration passes, the experiment scales down the ReplicaSets it created and marks the AnalysisRuns successful unless the
requiredForCompletion field is used in the Experiment. If enabled, the ReplicaSets are still scaled-down, but the Experiment does not finish until the Analysis Run finishes.
.spec.duration is an optional field. If it’s left unset, and the Experiment creates no AnalysisRuns, the ReplicaSets run indefinitely. The Experiment creates AnalysisRuns without the
requiredForCompletion field, the Experiment fails only when the AnalysisRun created fails or errors out. If the
requiredForCompletion field is set, the Experiment only marks itself as Successful and scales down the created ReplicaSets when the AnalysisRun finishes Successfully.
Additionally, an Experiment ends if the
.spec.terminate field is set to true regardless of the state of the Experiment.
Why doesn't my AnalysisRun end?¶
The AnalysisRun’s duration is controlled by the metrics specified. Each Metric can specify an interval, count, and various limits (ConsecutiveErrorLimit, InconclusiveLimit, FailureLimit). If the interval is omitted, the AnalysisRun takes a single measurement. The count indicates how many measurements should be taken and causes the AnalysisRun to run indefinitely if omitted. The ConsecutiveErrorLimit, InconclusiveLimit, and FailureLimit define the thresholds allowed before putting the rollout into a completed state.
Additionally, an AnalysisRun ends if the
.spec.terminate field is set to true regardless of the state of the AnalysisRun.
What is the difference between failures and errors?¶
Failures are when the failure condition evaluates to true or an AnalysisRun without a failure condition evaluates the success condition to false. Errors are when the controller has any kind of issue with taking a measurement (i.e. invalid Prometheus URL).