Skip to main content

Kubernetes: Node Time Like Show Time

The title was initially 'Bring Back the Node', but I didn't think people would get the reference. Applause if you did!




Making a deployment in the previous post made a POD for our application to be hosted in.

($POD_NAME variable)

Pods are an abstraction that represent 1 or more containers and shared resources for them, like Volumes, what the page describes as

‘Networking, as a unique cluster IP address’ (Sounds exciting, like a distant relative of subnetting or vlans)

 and instructions on  how to actually run the containers.





A Pod can hold the application and something that is closely coupled to it. The example given is a Node.js app and the data to be read by it.

Pods hold containers, and the containers share an IP address / Port space
Are co-located and scheduled, and
Run in a shared context on the same Node.

When we create a Deployment, that Deployment creates Pods with Containers inside of them.

The hierarchy reminds me a bit of Forests/Trees. Or Matryoshka dolls.

Pods run on Nodes, a virtual or physical worker machine in Kubernetes, and is managed by the Master.

Nodes = Multiple pods, Master schedules pods automatically across Nodes in the cluster.

Every Node runs at least a Kubelet and a container runtime, that pulls the container image from a registry, unpackets it, and runs it.

I’m just going to link to the image they provide. It looks like a cell.

So;

* Nodes hold pods and pods hold volumes and containerized apps.
* and there are some processes on the node.

Let’s troubleshoot with kubectl.

The syntax is kubectl [action]

- get [resource]; Lists resources
- describe; Show details about a resource
- logs; Print logs from a container
- exec; Execute a command on a podded container.
And those are what we’re going to be using in today’s tutorial!

Just putting in kubectl get with no specifics lists a lot of things.

Whoa nelly. 

adding pods gives us just the one.



But what’s in our pod? Describe it.


That’s not even all of the information!

Time to debug through a proxy in another terminal window.


We’re going to store this into the POD_NAME variable.

the curl request shows the output
{curl http://localhost:8001/api/vi/namespaces/default/pods/$POD_NAME/proxy}
The very long Pod name is in that variable, we don’t have to type it out, just $POD_NAME. Nice.

If there was more than one Pod, it wouldn't work.

What about our container logs? Let’s use
kubectl logs $POD_NAME


"Where are you running? WHERE are you running?"

Cool, now let’s execute a command.

The pod should be up and running, and we use the exec variable instead of get.



(env = enviroment variables, I think. I looked it up.)
(using SSL port 443)

Let’s start a bash in the Pod container with kubectl exec -ti $POD_NAME bash

Oh, we’ve moved to the root of our container! See the prompt over there?


 Now we can run the application with cat [where the source code is stored].
And check it again with a curl command. Close the container with an exit command.

Comments

Popular posts from this blog

Connecting IoT Devices to a Registration Server (Packet Tracer, Cisco)

In Packet Tracer, a demo software made by Cisco Systems. It certainly has changed a lot since 2016. It's almost an Olympic feat to even get started with it now, but it does look snazzy. This is for the new CCNA, that integrates, among other things, IoT and Automation, which I've worked on here before. Instructions here . I don't know if this is an aspect of "Let's make sure people are paying attention and not simply following blindly", or an oversight - The instructions indicate a Meraki Server, when a regular one is the working option here. I have to enable the IoT service on this server. Also, we assign the server an IPv4 address from a DHCP pool instead of giving it a static one. For something that handles our IoT business, perhaps that's safer; Getting a new IPv4 address every week or so is a minimal step against an intruder, but it is a step. There are no devices associated with this new server; In an earlier lab (not shown), I attached them to 'H

Securing Terraform and You Part 1 -- rego, Tfsec, and Terrascan

9/20: The open source version of Terraform is now  OpenTofu     Sometimes, I write articles even when things don't work. It's about showing a learning process.  Using IaC means consistency, and one thing you don't want to do is have 5 open S3 buckets on AWS that anyone on the internet can reach.  That's where tools such as Terrascan and Tfsec come in, where we can make our own policies and rules to be checked against our code before we init.  As this was contract work, I can't show you the exact code used, but I can tell you that this blog post by Cesar Rodriguez of Cloud Security Musings was quite helpful, as well as this one by Chris Ayers . The issue is using Rego; I found a cool VS Code Extension; Terrascan Rego Editor , as well as several courses on Styra Academy; Policy Authoring and Policy Essentials . The big issue was figuring out how to tell Terrascan to follow a certain policy; I made it, put it in a directory, and ran the program while in that directory

Building, Breaking, and Building A CRM with Retool

 I like no- or low-code solutions to things. I've often wanted to simply push a button or move some GUI around and have the code implement itself.  I've thought about building something that's like a customer relationship management (CRM) system for keeping up with my network better than my little spreadsheet where I click links and then go like something. The general idea in this CRM Development is:  To have a GUI to add people to a NRM (Network Relationship Management).       Attach it to a database (MySQL is what I went with eventually using Amazon Relational Database service, but you can use PostGRES, and probably others).     Make sure components are connected to each other in the retool interface. This video is a good start. Watching the tutorial video, heard some SQL commands and went 'Oh no 😳" before going "Wait I know basic SQL", which is good, because you'll see.  When you get set up, there's a plethora of resources you can use -- Incl