Kubernetes-How to send data from a pod to another pod in kubernetes

Question

In dockers, I had two containers Mosquitto abd userInfo

userInfo is a container which performs some logic and then send the result to mosquitto container. Mosquitto container then use this information to send it to IOT hub. To start these containers in Docker, I created a network and started both the container in the same network. So I can easily use the hostname of mosquitto container inside userinfo container to send data. I need to do this same in kubernetes.

So in kubernetes, what I did, I deployed the Mosquitto so its POD was created then I created its service and use it inside the userInfo pod to send data to mosquitto . But this is not working.

I created the service by using

kubectl expose deployment mosquitto

I need to send data of userInfo to Mosquitto .

• How can I achieve this.?

• Do I need to create network as I was doing in dockers or is there any other way.?

I also tried creating a pod with two containers ie mosquitto & userInfo , but this was also not working.

Thanks

Answer 1

A Kubernetes pod may contain multiple containers. People generally run multiple containers in a pod when the two containers are tightly coupled, and it sounds like this is what you're looking for. These containers are guaranteed to be hosted on the same machine (they can contact each other via localhost), share the same port space, and can also use the same volumes. https://kubernetes.io/docs/concepts/workloads/pods/pod/#what-is-a-pod

Answer 2

Two containers same POD

If you are interested in the communication between two containers belonging to the same POD there is the guide from the official documentation showing how to achieve this through shared volumes.

The primary reason that Pods can have multiple containers is to support helper applications that assist a primary application. Typical examples of helper applications are data pullers, data pushers, and proxies. Helper and primary applications often need to communicate with each other. Typically this is done through a shared filesystem, as shown in this exercise, or through the loopback network interface, localhost.

Try to avoid to place two container in the same POD if you do not need it. Additional information can be found here: Multi-container pods and container communication in Kubernetes .

Two containers two POD

In this case (you can do the same also for the previous case) the best way to proceed is to expose a through a service the listening process of the container.

In this way you will be able to rely always on the very same IP or domain name (that you will be able to resolve merely internally) and port. For example , if you have a Service called "my-service" in Kubernetes Namespace "my-ns" a DNS record for "my-service.my-ns" is created.

The network part is managed by Kubernetes so you will not need to do anything(in the basic configurations), merely when creating the service to instruct which is the target port of the container and the port that the client should use and the mapping is automatic.

Then once you exposed a port and an IP how you implement the communication and the datatransfer is no longer a Kubernetes question. You can implement it thorough a web server having static contents, through FTP, having a script sending SCP commands, basically there are infinite ways to do it.