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kube-2019-
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10
k8s/just-a-pod.yaml
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k8s/just-a-pod.yaml
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apiVersion: v1
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Kind: Pod
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metadata:
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name: hello
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namespace: default
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spec:
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containers:
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- name: hello
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image: nginx
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1
slides/_redirects
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1
slides/_redirects
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/ /kube-twodays.yml.html 200!
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237
slides/k8s/staticpods.md
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slides/k8s/staticpods.md
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# Static pods
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- Hosting the Kubernetes control plane on Kubernetes has advantages:
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- we can use Kubernetes' replication and scaling features for the control plane
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- we can leverage rolling updates to upgrade the control plane
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- However, there is a catch:
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- deploying on Kubernetes requires the API to be available
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- the API won't be available until the control plane is deployed
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- How can we get out of that chicken-and-egg problem?
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---
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## A possible approach
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- Since each component of the control plane can be replicated ...
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- We could set up the control plane outside of the cluster
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- Then, once the cluster is fully operational, create replicas running on the cluster
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- Finally, remove the replicas that are running outside of the cluster
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*What could possibly go wrong?*
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---
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## Sawing off the branch you're sitting on
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- What if anything goes wrong?
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(During the setup or at a later point)
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- Worst case scenario, we might need to:
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- set up a new control plane (outside of the cluster)
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- restore a backup from the old control plane
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- move the new control plane to the cluster (again)
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- This doesn't sound like a great experience
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---
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## Static pods to the rescue
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- Pods are started by kubelet (an agent running on every node)
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- To know which pods it should run, the kubelet queries the API server
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- The kubelet can also get a list of *static pods* from:
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- a directory containing one (or multiple) *manifests*, and/or
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- a URL (serving a *manifest*)
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- These "manifests" are basically YAML definitions
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(As produced by `kubectl get pod my-little-pod -o yaml --export`)
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---
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## Static pods are dynamic
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- Kubelet will periodically reload the manifests
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- It will start/stop pods accordingly
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(i.e. it is not necessary to restart the kubelet after updating the manifests)
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- When connected to the Kubernetes API, the kubelet will create *mirror pods*
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- Mirror pods are copies of the static pods
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(so they can be seen with e.g. `kubectl get pods`)
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---
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## Bootstrapping a cluster with static pods
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- We can run control plane components with these static pods
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- They can start without requiring access to the API server
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- Once they are up and running, the API becomes available
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- These pods are then visible through the API
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(We cannot upgrade them from the API, though)
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*This is how kubeadm has initialized our clusters.*
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---
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## Static pods vs normal pods
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- The API only gives us a read-only access to static pods
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- We can `kubectl delete` a static pod ...
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... But the kubelet will restart it immediately
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- Static pods can be selected just like other pods
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(So they can receive service traffic)
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- A service can select a mixture of static and other pods
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---
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## From static pods to normal pods
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- Once the control plane is up and running, it can be used to create normal pods
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- We can then set up a copy of the control plane in normal pods
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- Then the static pods can be removed
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- The scheduler and the controller manager use leader election
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(Only one is active at a time; removing an instance is seamless)
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- Each instance of the API server adds itself to the `kubernetes` service
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- Etcd will typically require more work!
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---
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## From normal pods back to static pods
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- Alright, but what if the control plane is down and we need to fix it?
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- We restart it using static pods!
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- This can be done automatically with the [Pod Checkpointer]
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- The Pod Checkpointer automatically generates manifests of running pods
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- The manifests are used to restart these pods if API contact is lost
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(More details in the [Pod Checkpointer] documentation page)
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- This technique is used by [bootkube]
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[Pod Checkpointer]: https://github.com/kubernetes-incubator/bootkube/blob/master/cmd/checkpoint/README.md
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[bootkube]: https://github.com/kubernetes-incubator/bootkube
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---
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## Where should the control plane run?
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*Is it better to run the control plane in static pods, or normal pods?*
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- If I'm a *user* of the cluster: I don't care, it makes no difference to me
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- What if I'm an *admin*, i.e. the person who installs, upgrades, repairs... the cluster?
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- If I'm using a managed Kubernetes cluster (AKS, EKS, GKE...) it's not my problem
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(I'm not the one setting up and managing the control plane)
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- If I already picked a tool (kubeadm, kops...) to set up my cluster, the tool decides for me
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- What if I haven't picked a tool yet, or if I'm installing from scratch?
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- static pods = easier to set up, easier to troubleshoot, less risk of outage
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- normal pods = easier to upgrade, easier to move (if nodes need to be shut down)
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---
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## Static pods in action
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- On our clusters, the `staticPodPath` is `/etc/kubernetes/manifests`
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.exercise[
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- Have a look at this directory:
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```bash
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ls -l /etc/kubernetes/manifests
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```
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]
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We should see YAML files corresponding to the pods of the control plane.
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---
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## Running a static pod
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- We are going to add a pod manifest to the directory, and kubelet will run it
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.exercise[
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- Copy a manifest to the directory:
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```bash
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sudo cp ~/container.training/k8s/just-a-pod.yaml /etc/kubernetes/manifests
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```
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- Check that it's running:
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```bash
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kubectl get pods
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```
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]
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The output should include a pod named `hello-node1`.
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---
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## Remarks
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In the manifest, the pod was named `hello`.
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```yaml
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apiVersion: v1
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Kind: Pod
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metadata:
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name: hello
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namespace: default
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spec:
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containers:
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- name: hello
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image: nginx
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```
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The `-node1` suffix was added automatically by kubelet.
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If we delete the pod (with `kubectl delete`), it will be recreated immediately.
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To delete the pod, we need to delete (or move) the manifest file.
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@@ -58,6 +58,7 @@ chapters:
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- k8s/extending-api.md
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- k8s/statefulsets.md
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- k8s/portworx.md
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- k8s/staticpods.md
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- - k8s/whatsnext.md
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- k8s/links.md
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- shared/thankyou.md
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@@ -1,14 +1,12 @@
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title: |
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Deploying and Scaling Microservices
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Deploying and Scaling Applications
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with Kubernetes
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#chat: "[Slack](https://dockercommunity.slack.com/messages/C7GKACWDV)"
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#chat: "[Gitter](https://gitter.im/jpetazzo/workshop-yyyymmdd-city)"
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chat: "In person!"
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chat: "[Gitter](https://gitter.im/enix/formation-kubernetes-20190128)"
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gitrepo: github.com/jpetazzo/container.training
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slides: http://container.training/
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slides: http://kube-2019-02.container.training/
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exclude:
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- self-paced
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@@ -48,16 +46,14 @@ chapters:
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- k8s/netpol.md
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- k8s/authn-authz.md
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- - k8s/ingress.md
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- k8s/gitworkflows.md
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- k8s/prometheus.md
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- - k8s/volumes.md
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- k8s/build-with-docker.md
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- k8s/build-with-kaniko.md
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- k8s/configuration.md
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- - k8s/owners-and-dependents.md
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- k8s/extending-api.md
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- k8s/owners-and-dependents.md
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- - k8s/extending-api.md
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- k8s/statefulsets.md
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- k8s/portworx.md
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- k8s/staticpods.md
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- - k8s/whatsnext.md
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- k8s/links.md
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- shared/thankyou.md
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@@ -1,30 +1,10 @@
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## Intros
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- This slide should be customized by the tutorial instructor(s).
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- Hello! I'm Jérôme ([@jpetazzo](https://twitter.com/jpetazzo), Enix SAS)
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- Hello! We are:
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- The workshop will run from 9am to 5pm
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- .emoji[👩🏻🏫] Ann O'Nymous ([@...](https://twitter.com/...), Megacorp Inc)
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- .emoji[👨🏾🎓] Stu Dent ([@...](https://twitter.com/...), University of Wakanda)
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<!-- .dummy[
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- .emoji[👷🏻♀️] AJ ([@s0ulshake](https://twitter.com/s0ulshake), Travis CI)
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- .emoji[🚁] Alexandre ([@alexbuisine](https://twitter.com/alexbuisine), Enix SAS)
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- .emoji[🐳] Jérôme ([@jpetazzo](https://twitter.com/jpetazzo), Enix SAS)
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- .emoji[⛵] Jérémy ([@jeremygarrouste](twitter.com/jeremygarrouste), Inpiwee)
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- .emoji[🎧] Romain ([@rdegez](https://twitter.com/rdegez), Enix SAS)
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] -->
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- The workshop will run from ...
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- There will be a lunch break at ...
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- There will be a lunch break around noon
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(And coffee breaks!)
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17
slides/override.css
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17
slides/override.css
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.remark-slide-content:not(.pic) {
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background-repeat: no-repeat;
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background-position: 99% 1%;
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background-size: 8%;
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background-image: url(https://enix.io/static/img/logos/logo-domain-cropped.png);
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}
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div.extra-details:not(.pic) {
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background-image: url("images/extra-details.png"), url(https://enix.io/static/img/logos/logo-domain-cropped.png);
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background-position: 0.5% 1%, 99% 1%;
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background-size: 4%, 8%;
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}
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.remark-slide-content:not(.pic) div.remark-slide-number {
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top: 16px;
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right: 112px
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}
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@@ -11,11 +11,7 @@ class: title, in-person
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@@TITLE@@<br/></br>
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.footnote[
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**Be kind to the WiFi!**<br/>
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<!-- *Use the 5G network.* -->
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*Don't use your hotspot.*<br/>
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*Don't stream videos or download big files during the workshop[.](https://www.youtube.com/watch?v=h16zyxiwDLY)*<br/>
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*Thank you!*
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[.](https://www.youtube.com/watch?v=h16zyxiwDLY)
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**Slides: @@SLIDES@@**
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]
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@@ -4,6 +4,7 @@
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<title>@@TITLE@@</title>
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<meta http-equiv="Content-Type" content="text/html; charset=UTF-8"/>
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<link rel="stylesheet" href="workshop.css">
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<link rel="stylesheet" href="override.css">
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</head>
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<body>
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<!--
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Reference in New Issue
Block a user