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164 lines
3.5 KiB
Markdown
164 lines
3.5 KiB
Markdown
# Accessing logs from the CLI
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- The `kubectl logs` command has limitations:
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- it cannot stream logs from multiple pods at a time
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- when showing logs from multiple pods, it mixes them all together
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- We are going to see how to do it better
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---
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## Doing it manually
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- We *could* (if we were so inclined) write a program or script that would:
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- take a selector as an argument
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- enumerate all pods matching that selector (with `kubectl get -l ...`)
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- fork one `kubectl logs --follow ...` command per container
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- annotate the logs (the output of each `kubectl logs ...` process) with their origin
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- preserve ordering by using `kubectl logs --timestamps ...` and merge the output
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--
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- We *could* do it, but thankfully, others did it for us already!
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---
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## Stern
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[Stern](https://github.com/stern/stern) is an open source project
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originally by [Wercker](http://www.wercker.com/).
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From the README:
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*Stern allows you to tail multiple pods on Kubernetes and multiple containers within the pod. Each result is color coded for quicker debugging.*
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*The query is a regular expression so the pod name can easily be filtered and you don't need to specify the exact id (for instance omitting the deployment id). If a pod is deleted it gets removed from tail and if a new pod is added it automatically gets tailed.*
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Exactly what we need!
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---
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## Checking if Stern is installed
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- Run `stern` (without arguments) to check if it's installed:
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```
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$ stern
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Tail multiple pods and containers from Kubernetes
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Usage:
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stern pod-query [flags]
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```
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- If it's missing, let's see how to install it
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---
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## Installing Stern
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- Stern is written in Go
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- Go programs are usually very easy to install
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(no dependencies, extra libraries to install, etc)
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- Binary releases are available [on GitHub][stern-releases]
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- Stern is also available through most package managers
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(e.g. on macOS, we can `brew install stern` or `sudo port install stern`)
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[stern-releases]: https://github.com/stern/stern/releases
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---
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## Using Stern
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- There are two ways to specify the pods whose logs we want to see:
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- `-l` followed by a selector expression (like with many `kubectl` commands)
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- with a "pod query," i.e. a regex used to match pod names
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- These two ways can be combined if necessary
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.lab[
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- View the logs for all the pingpong containers:
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```bash
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stern pingpong
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```
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<!--
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```wait seq=```
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```key ^C```
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-->
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]
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---
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## Stern convenient options
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- The `--tail N` flag shows the last `N` lines for each container
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(Instead of showing the logs since the creation of the container)
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- The `-t` / `--timestamps` flag shows timestamps
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- The `--all-namespaces` flag is self-explanatory
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.lab[
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- View what's up with the `weave` system containers:
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```bash
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stern --tail 1 --timestamps --all-namespaces weave
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```
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<!--
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```wait weave-npc```
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```key ^C```
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-->
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]
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---
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## Using Stern with a selector
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- When specifying a selector, we can omit the value for a label
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- This will match all objects having that label (regardless of the value)
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- Everything created with `kubectl run` has a label `run`
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- Everything created with `kubectl create deployment` has a label `app`
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- We can use that property to view the logs of all the pods created with `kubectl create deployment`
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.lab[
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- View the logs for all the things started with `kubectl create deployment`:
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```bash
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stern -l app
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```
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<!--
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```wait seq=```
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```key ^C```
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-->
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]
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???
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:EN:- Viewing pod logs from the CLI
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:FR:- Consulter les logs des pods depuis la CLI
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