Namespaces

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Example Notes

In some cases, you want to divide your resources, provide different access rights to those resources and more. This is largely driven by the fear that something could happen to your precious production resources.

However, with every new cluster, the management complexity will scale — the more clusters you have, the more you have to manage — basically, the resource overhead of many small clusters is higher than of one big one. Think about this in terms of houses, if you have one big house, you have to take care of a lot but having several small houses, you have x the number of everything + they will be affected by different conditions.

Practical

Let's get moving, you only learn by doing.

Clone this repository https://github.com/vfarcic/k8s-specs 

cd k8s-specs

and then, we will use this application

cat ns/go-demo-2.yml

Then we do a nasty work-around to specify the image tag used in the pod

IMG=vfarcic/go-demo-2

TAG=1.0

cat ns/go-demo-2.yml \
| sed -e \
"s@image: $IMG@image: $IMG:$TAG@g" \
| kubectl create -f -

When the -f argument is followed with a dash (-), kubectl uses standard input (stdin) instead of a file.

To confirm that the deployment was successful 

kubectl rollout status \
2 deploy go-demo-2-api

Which will get us the following output

hello, release 1.0!

Almost every service are Kubernetes Objects. 

kubectl get all

Gives us a full list of all the resources that we currently have up and running.

The system-level objects within our cluster are usually not visible, only the objects that we created.

Within the same namespace, we cannot have twice the same object with exactly the same name. However, we can have the same object in two different namespaces.

Additionally, you could specify within a cluster permissions, quotas, policies, and more — will look at those sometimes later within the challenge.

We can list all of our namespaces through

kubectl get ns

Create a new namespaces

kubectl create namespace testing

Note that you could also use 'ns' for 'namespace'

Kubernetes puts all the resources needed to execute Kubernetes commands into the kube-system namespace

kubectl --namespace kube-system get all

Now that we have a namespace testing, we can use it for new deployments — however, specifying the namespace with each command is annoying. What we can do instead is

kubectl config set-context testing \
 --namespace testing \
 --cluster docker-desktop \
 --user docker-desktop

In this case, you will have to change the command according to your cluster. The created context uses the same cluster as before — just a different namespace.

You can view the config with the following command

kubectl config view

Once we have a new context, we can switch to that one

kubectl config use-context testing

Once done, all of our commands will be automatically executed in the testing namespace.

Now we can deploy the same resource as before but specify a different tag.

TAG=2.0

DOM=go-demo-2.com

cat ns/go-demo-2.yml \
| sed -e \
"s@image: $IMG@image: $IMG:$TAG@g" \
| sed -e \
"s@host: $DOM@host: $TAG\.$DOM@g" \
| kubectl create -f -

to confirm that the rollout has finished

kubectl rollout status \
deployment go-demo-2-api

Now we can send requests to the different namespaces 

curl -H "Host: 2.0.go-demo-2.com" \
2 "http://$(minikube ip)/demo/hello"

Deleting resources

It can be really annoying to have to delete all objects one by one. What we can do instead is to delete all resources within a namespace all at once 

kubectl delete ns testing

The real magic of namespaces is when we combine those with authorization logic, which we are going to be looking at in later videos.