In this tutorial we’ll explore how to use health rules to let users know if their supply chain is working correctly. We’ll see how the different types of resources you create in a supply chain effects what health rules are appropriate.
For this tutorial you will need a kubernetes cluster with Cartographer installed. You may follow the installation instructions here.
Alternatively, you may choose to use the ./hack/setup.sh script to install a kind cluster with Cartographer. This script is meant for our end-to-end testing and while we rely on it working in that role, no user guarantees are made about the script.
Command to run from the Cartographer directory:
$ ./hack/setup.sh cluster cartographer-latest
If you later wish to tear down this generated cluster, run
$ ./hack/setup.sh teardown
In previous tutorials, we’ve split the personas between app operator and app developer. Now we will split the personas between authors and users.
A template author is the expert on some kubernetes resource (e.g. Pods, kpack Images, Knative Services). They understand the behavior of the resource and the fields in the resource’s spec and status. It is their responsibility to write a Cartographer template that wraps their resource.
Supply Chain Author
A supply chain author is the organization’s expert on organizational policy. They know what steps must happen to take source code and verify that it is ready for deployment on a cluster. (There are no special steps for supply chain authors in this tutorial, but they are mentioned for completeness)
A user will be any persona that is interested in what happens when a workload is applied to the cluster. Often this is the app developer persona, who has created a workload and wants to know that their code has reached production. This can also be the app operator persona, who knows that some devs have workloads and wants to know that changes are smoothly reaching production.
At the Hello World Application Inc., we’ve observed that not all workloads are providing valid configuration, leading to supply chains that cannot stamp out k8s deployments. We want to make sure that in this case, the workload object reflects the problem. We will add health rules to the template that we created in “Build Your First Supply Chain”.
Template Author Steps
Previously, we created a Supply Chain with just one step: it creates a deployment. As template authors it is our responsibility to be experts on the resource we template out. Let’s review just a few details that will be important to remember about kubernetes deployments:
- A deployment creates a replicaset, which in turn creates pods.
- A deployment status has conditions. Read more on k8s conditions.
- The deployment condition “Available” reports whether the declared number of pod replicas are available on the cluster.
- The deployment condition “Progressing” reports whether the managed replicasets are making progress in creating pods.
- The progressing condition will change from True to False if the timeout set in the deployment’s
spec.progressDeadlineSecondsfield is exceeded.
For a more thorough review of Deployments, see the kubernetes documentation.
We’ll start by setting a progress deadline. We’ll set a timeout of 30 seconds because this is a demo (we’re not
suggesting this is the appropriate value for the real world). In the
template field of our cluster template we see our
deployment. There we can see the new
apiVersion: carto.run/v1alpha1 kind: ClusterTemplate metadata: name: app-deploy spec: template: apiVersion: apps/v1 kind: Deployment metadata: name: $(workload.metadata.name)$-deployment labels: app: $(workload.metadata.name)$ spec: progressDeadlineSeconds: 30 # <=== NEW CONFIG replicas: 3 selector: matchLabels: app: $(workload.metadata.name)$ template: metadata: labels: app: $(workload.metadata.name)$ spec: containers: - name: $(workload.metadata.name)$ image: $(workload.spec.image)$
Next we’ll write our health rule. When the workload reports the health of the deployment we’ll report if healthy is " True", “False”, or “Unknown”. Deployments have two conditions, progressing and available that report “True” or “False”. Let’s consider how we’ll want to represent each of these states:
|Available||Progressing||Workload Reports Healthy as:||Reason|
|True||True||True||Pods are all available and any updates necessary are progressing properly|
|True||False||False||There are pods available, but the necessary updates (changes our workload expects) aren’t progressing|
|False||True||Unknown||The expected pods are not available, but work is progressing and may resolve|
|False||False||False||The expected pods are not available, and necessary updates aren’t progressing|
From this we know that Workload should report the Deployment as Healthy when both available and progressing are true. It should report False whenever progressing is False. And report unknown otherwise. With this in mind, we’re ready to write our healthrule.
Because health of a Deployment depends on more than one condition, we’ll write a multimatch health rule. A multimatch rule requires that we define what constitutes both healthy and unhealthy. (Good thing we just determined that above!) For both healthy and unhealthy we’ll specify a set of matchers. If all the healthy matchers are satisfied, we’ll report healthy == True. If any of the unhealthy matchers are satisfied, we’ll report healthy == False. Otherwise, we’ll report healthy == Unknown.
apiVersion: carto.run/v1alpha1 kind: ClusterTemplate spec: ... healthRule: multiMatch: healthy: # Matchers are ANDed unhealthy: # Matchers are ORed
Note: Health rules are available on all Carto templates (e.g. ClusterSourceTemplate, ClusterImageTemplate, etc).
Let’s begin with the healthy matchers. Two different conditions on a Deployment must be true for it to be healthy. We
can write these as
matchConditions. We just need to provide the conditions'
healthy: matchConditions: - type: Available status: 'True' - type: Progressing status: 'True'
And we can write the unhealthy matcher:
unhealthy: matchConditions: - type: Progressing status: 'False'
Let’s bring this all together and look at the template we’ll apply to the cluster:
--- apiVersion: carto.run/v1alpha1 kind: ClusterTemplate metadata: name: app-deploy spec: template: apiVersion: apps/v1 kind: Deployment metadata: name: $(workload.metadata.name)$-deployment labels: app: $(workload.metadata.name)$ spec: progressDeadlineSeconds: 30 replicas: 3 selector: matchLabels: app: $(workload.metadata.name)$ template: metadata: labels: app: $(workload.metadata.name)$ spec: containers: - name: $(workload.metadata.name)$ image: $(workload.spec.image)$ healthRule: multiMatch: healthy: matchConditions: - type: Available status: 'True' - type: Progressing status: 'True' unhealthy: matchConditions: - type: Progressing status: 'False'
Otherwise we’ll apply the same app operator objects (supply chain, service account, role, role binding) from the “Build Your First Supply Chain” tutorial.
App Dev Steps
Let’s apply a workload that we know will succeed, as we’ve used it before:
--- apiVersion: carto.run/v1alpha1 kind: Workload metadata: name: hello labels: workload-type: pre-built spec: image: docker.io/nginxdemos/hello:latest
We’ve seen this workload and supply chain before, so we know what objects will be created (a deployment, which will create a replicaset, which will create pods). What is different in this tutorial is the status of the workload itself.
Let’s observe the workload after giving a moment for the deployment’s pods to come up.
$ kubectl get -o yaml workload hello
First let’s consider the
status: ... resources: - name: deploy conditions: - type: ResourceSubmitted status: "True" reason: ResourceSubmissionComplete - type: Healthy status: True reason: MatchedCondition message: 'condition status: True, message: Deployment has minimum availability.' - reason: Ready status: Unknown type: Ready
Look at that second condition! Healthy is true. Our matchers were satisfied. Great stuff.
Next let’s look at the top level conditions of the workload and concentrate on the condition with type
status: conditions: - reason: HealthyConditionRule status: True type: ResourcesHealthy
This condition on the workload aggregates the health of all the objects created by the workload. If all are healthy, the
condition is true. If any are unhealthy, the condition is False. Otherwise the condition is Unknown. In our case, the
aggregation is trivial to compute; the workload’s
ResourcesHealthy condition is true.
Steps of an unfortunate dev
At some point, each of us will make a mistake, like mistyping the name of an image in our workload. Let’s try submitting the following workload:
--- apiVersion: carto.run/v1alpha1 kind: Workload metadata: name: typo labels: workload-type: pre-built spec: image: docker.io/what-a-typo-this-image-definitely-does-not-exist/hello-world:latest
We’ll see what feedback we get in the workload status.
First, we’ll check the workload just after deploying, inspecting the
$ kubectl get -o yaml workload typo
status: resources: - conditions: - type: ResourceSubmitted status: "True" reason: ResourceSubmissionComplete - type: Healthy status: Unknown reason: NoMatchesFulfilled - type: Ready status: Unknown reason: NoMatchesFulfilled
From our discussion above, we know that the deployment will never reach a healthy state, but until it hits the timeout it will continue to report that it is progressing but the expected pods are not available. We can observe this directly:
$ kubectl get -o yaml deployment typo-deployment
apiVersion: apps/v1 kind: Deployment status: conditions: - message: Deployment does not have minimum availability. reason: MinimumReplicasUnavailable status: "False" type: Available ... - message: ReplicaSet "hello-deployment-SOMEHASH" is progressing. reason: ReplicaSetUpdated status: "True" type: Progressing ...
Let’s check back in on the deployment status after 30 seconds:
- message: Deployment does not have minimum availability. reason: MinimumReplicasUnavailable status: "False" type: Available - message: ReplicaSet "typo-deployment-SOMEHASH" has timed out progressing. reason: ProgressDeadlineExceeded status: "False" type: Progressing
We see that the Progressing condition has switched to
Let’s verify that our workload healthy condition is reflecting this. We’ll observe
status: resources: - conditions: ... - type: Healthy status: "False" message: 'condition status: False, message: ReplicaSet "typo-deployment-7b8bd888d8" has timed out progressing.' reason: MatchedCondition
We see that
status.resources reports that an unhealthy condition matcher was satisfied. The
message of that
condition on the deployment is reflected in the workload’s status.resources[x].conditions[x].message field.
And we cn observe that the workload’s top level conditions then mirror this message in the
status: conditions: ... - type: ResourcesHealthy status: "False" message: 'condition status: False, message: ReplicaSet "typo-deployment-7b8bd888d8" has timed out progressing.' reason: HealthyConditionRule
Congratulations, you’ve used a healthrule to make your supply chain more understandable and repairable! You’ve learned:
- How to specify a multimatch rule with matchConditions matchers
- How to read the workload’s
- How to read the workload’s
To learn more, read the troubleshooting guide on ResourcesHealthy. It explores the possible values you’ll see and their meanings.
Also check out the reference page for the template CRDs
And read this blog post on an example resource for which determining a health rule is currently not possible!