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b56e54eaec
Now that we have a good number of longer exercises, it makes sense to rename the shorter demos/labs into 'labs' to avoid confusion between the two.
227 lines
3.9 KiB
Markdown
227 lines
3.9 KiB
Markdown
# Labels and annotations
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- Most Kubernetes resources can have *labels* and *annotations*
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- Both labels and annotations are arbitrary strings
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(with some limitations that we'll explain in a minute)
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- Both labels and annotations can be added, removed, changed, dynamically
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- This can be done with:
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- the `kubectl edit` command
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- the `kubectl label` and `kubectl annotate`
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- ... many other ways! (`kubectl apply -f`, `kubectl patch`, ...)
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---
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## Viewing labels and annotations
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- Let's see what we get when we create a Deployment
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.lab[
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- Create a Deployment:
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```bash
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kubectl create deployment clock --image=jpetazzo/clock
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```
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- Look at its annotations and labels:
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```bash
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kubectl describe deployment clock
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```
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]
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So, what do we get?
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---
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## Labels and annotations for our Deployment
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- We see one label:
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```
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Labels: app=clock
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```
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- This is added by `kubectl create deployment`
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- And one annotation:
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```
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Annotations: deployment.kubernetes.io/revision: 1
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```
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- This is to keep track of successive versions when doing rolling updates
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---
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## And for the related Pod?
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- Let's look up the Pod that was created and check it too
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.lab[
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- Find the name of the Pod:
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```bash
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kubectl get pods
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```
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- Display its information:
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```bash
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kubectl describe pod clock-xxxxxxxxxx-yyyyy
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```
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]
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So, what do we get?
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---
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## Labels and annotations for our Pod
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- We see two labels:
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```
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Labels: app=clock
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pod-template-hash=xxxxxxxxxx
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```
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- `app=clock` comes from `kubectl create deployment` too
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- `pod-template-hash` was assigned by the Replica Set
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(when we will do rolling updates, each set of Pods will have a different hash)
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- There are no annotations:
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```
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Annotations: <none>
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```
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---
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## Selectors
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- A *selector* is an expression matching labels
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- It will restrict a command to the objects matching *at least* all these labels
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.lab[
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- List all the pods with at least `app=clock`:
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```bash
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kubectl get pods --selector=app=clock
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```
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- List all the pods with a label `app`, regardless of its value:
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```bash
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kubectl get pods --selector=app
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```
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]
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---
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## Settings labels and annotations
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- The easiest method is to use `kubectl label` and `kubectl annotate`
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.lab[
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- Set a label on the `clock` Deployment:
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```bash
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kubectl label deployment clock color=blue
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```
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- Check it out:
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```bash
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kubectl describe deployment clock
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```
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]
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---
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## Other ways to view labels
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- `kubectl get` gives us a couple of useful flags to check labels
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- `kubectl get --show-labels` shows all labels
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- `kubectl get -L xyz` shows the value of label `xyz`
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.lab[
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- List all the labels that we have on pods:
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```bash
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kubectl get pods --show-labels
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```
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- List the value of label `app` on these pods:
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```bash
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kubectl get pods -L app
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```
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]
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---
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class: extra-details
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## More on selectors
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- If a selector has multiple labels, it means "match at least these labels"
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Example: `--selector=app=frontend,release=prod`
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- `--selector` can be abbreviated as `-l` (for **l**abels)
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We can also use negative selectors
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Example: `--selector=app!=clock`
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- Selectors can be used with most `kubectl` commands
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Examples: `kubectl delete`, `kubectl label`, ...
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---
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## Other ways to view labels
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- We can use the `--show-labels` flag with `kubectl get`
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.lab[
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- Show labels for a bunch of objects:
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```bash
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kubectl get --show-labels po,rs,deploy,svc,no
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```
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]
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---
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## Differences between labels and annotations
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- The *key* for both labels and annotations:
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- must start and end with a letter or digit
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- can also have `.` `-` `_` (but not in first or last position)
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- can be up to 63 characters, or 253 + `/` + 63
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- Label *values* are up to 63 characters, with the same restrictions
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- Annotations *values* can have arbitrary characters (yes, even binary)
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- Maximum length isn't defined
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(dozens of kilobytes is fine, hundreds maybe not so much)
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???
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:EN:- Labels and annotations
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:FR:- *Labels* et annotations
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