commit 52bef5718d92e540ab9f1ddc15467375329d7328
parent f2f4276e9e383b250bd052d8cf17b1163bb9afb6
Author: Alex Balgavy <alex@balgavy.eu>
Date: Sat, 22 Jan 2022 18:58:28 +0100
Update software containerisation notes
Diffstat:
3 files changed, 56 insertions(+), 0 deletions(-)
diff --git a/content/softcont-notes/_index.md b/content/softcont-notes/_index.md
@@ -11,3 +11,5 @@ title = 'Software Containerisation'
7. [Storage](storage)
8. [StatefulSet](statefulset)
9. [ConfigMaps & Secrets](configmaps-secrets)
+10. [Deployment updates](deployment-updates)
+11. [Helm: Kubernetes package manager](helm)
diff --git a/content/softcont-notes/deployment-updates.md b/content/softcont-notes/deployment-updates.md
@@ -0,0 +1,28 @@
++++
+title = 'Deployment updates'
++++
+# Deployment updates
+## Rolling updates
+If you change Deployment's pod template (`.spec.template`), deployment rollout is triggered.
+To observe rollout, you can use e.g. `kubectl rollout status <deployment>`
+
+Each pod and ReplicaSet created by Deployment controller get the same `pod-template-hash` label.
+That's generated by hashing PodTemplate of ReplicaSet.
+Its purpose is to ensure that ReplicaSets created from Deployment don't overlap.
+
+So that the application remains available, Deployment ensures that:
+- 25% max unavailable: at most 25% of desired number of Pods are down
+- 25% max surge: at most 25% more than desired number of pods are up
+
+You can check `kubectl rollout history`. To save a change cause, use the parameter `--record`.
+
+To roll back, use `kubectl rollout undo --to-revision=n`
+
+## Canary Deployments
+Problem with rolling updates is while it's happening, you have no way of testing that it's working fine.
+
+Canary Deployments are used to test new release with subset of users before propagating to all users.
+
+Involves using at least on Service to direct traffic to pods that run old code or pods that run new code.
+You add a label to pods, indicating whether it's the original type or canary.
+If service does not discriminate based on that label, then both types of pods get traffic directed to them.
diff --git a/content/softcont-notes/helm.md b/content/softcont-notes/helm.md
@@ -0,0 +1,26 @@
++++
+title = 'Helm: Kubernetes package manager'
++++
+## Helm: Kubernetes package manager
+Introduces Helm chart, which describes contents of all objects in the application using a single package.
+A running instance of such a set of Kubernetes objects is a "release".
+Helm charts are stored in repos.
+Helm must be installed separately from Kubernetes.
+
+From end user POV, on microk8s you do `microk8s enable helm3`, and then use it like a standard package manager (i.e. `list`, `install`, `uninstall`...)
+
+### Creating charts
+A chart can include other charts.
+A chart contains `Chart.yaml`, a `values.yaml`, and a templates folder.
+
+Start by running `helm create <chart-name>`, which gives you a starting skeleton:
+- `Chart.yaml`: mandatory. `type` field can be `application` (deployed standalone), or `library` (deployed as dependencies of other apps).
+ - dependencies may include `tags` (list of labels) and `conditions` (one or more YAML paths, and the chart can be enabled/disabled based on their values in the top-level `values.yaml`)
+- `templates/`: YAML template files defined with the syntax of Go templates. You can see what's generated with e.g. `helm install --dry-run --debug <chart-path> --generate-name`
+- `service.yaml`: uses Helm-specific objects `.Chart` (metadata like name and version) and `.Values` (exposes config that can be set at `helm install` time using `--set yaml.path=value`)
+ - `.Values` can come from the chart's `values.yaml` or that of a parent chart, or a values flag passed via `helm install -f newvalues.yaml`, or individual values passed via `helm install --set path=value`
+
+Then, you can install it with `helm install <release-name> <chart-dir>`, and see that it's installed with `helm ls`.
+
+To package it, do `helm package <chart-dir>`.
+You can upgrade a release with `helm upgrade <release-name> <chart-package-tgz>`, and downgrade with `helm rollback <release-name> <revision>`.
