Kubernetes: Pods

In previous articles, we have seen that containers are ” abstractplaces where applications run in the form of images.

PODs are the aggregation of multiple containers .

A service is the aggregation of several PODs .

The image in figure 1 shows the concept just explained.

Figure 1


All applications (images) present within the same POD will have the same (shared) IP address and the same Hostname (UTS NameSpace).

Communication between containers within the same HOST occurs through POSIX or System V IPCs

Now imagine you want to provide the ” the-gable-svc ” service, built with two images (containers): a Database and a Front-End.

During the design phase, is it better to design a single POD that contains the two containers ( figure 2 ) or two PODs with a container each ( figure 3 )? ( 1POD x 2 CONTAINER or 2 POD x 1 CONTAINER )

Figure 2

Figure 3

To answer accurately, you need to understand which application needs the most scalability and flexibility.

In our example it is the DB that could require more resources (RAM & CPU) to manage access peaks.

If I had designed a single POD, the increase in resources would involve both applications, effectively not optimizing energy expenditure.

Note 1: CPU & RAM resources are allocated during POD creation.

Is it always better to create more PODs?

This latter statement does not align with K8s’ resilience policy, where PODs should run on different physical hosts ( k8s is a cluster).

To resolve the demise, there is a good rule :

If the service works fine even though the PODs are spread across multiple hosts, then it is better to use multiple PODs (Figure 2).

Figure 4 shows the contents of the mysql-pod.yaml file that creates the POD for the mySQL application.

Figure 4

Let’s see the basic POD management syntax:

  • To start it just run the command: kubectl apply -f mysql-pod.yaml
  • To check its status: kubectl get pods
  • To get all the details: kubectl describe pods some-mysql
  • If we wanted to delete it: kubectl delete -f mysql-pod.yaml

For today it’s all in a little bit where we will talk about Access to the POD, how to copy files and much more.


Modern Applications – Episod 4: Docker Compose – YAML

The topic of this article is understanding how to automatize the delivery of a micro-service.

In the previous one, I showed the flow process of a service. This flow requires typing a lot of commands to launch any single container.

Is there a way to automatize the entire process making it easier?

Yes, Docker-compose is a tool for defining and running an environment multi-container.

Docker-compose works with a describing file that includes all the configurations. The file has the extension YAML (human-readable data-serialization language).

After writing the YAML file (in this example it is named mypersonalfile.yaml), the syntax of the command is:

docker-compose -f mypersonalfile.yaml

Let’s see an easy example using the article I wrote in the last episode as a source.

I had to type all these commands to implement the service:

a. Mongo DB commands

b. Mongo Express commands

In their place,  it’s possible to use the following yaml file.


We will find yaml files again when writing about Kubernetes architecture and its protection.

That’s all for now, take care guys