Busybox Curl

This is part 7 in a series of blog posts covering my learning experience for the CKAD exam. You can find the other parts in the series here:

After a quick look at Ballerina earlier this week, let’s start our sprint towards the end of the CKAD series! In this part we’ll touch on Services and Networking, specifically covering these two exam objectives:

• Understand Services
• Demonstrate basic understanding of NetworkPolicies

A special note on NetworkPolicies: There is an inconsistency between Azure and Calico NetworkPolicies on AKS. I have a seperate post explaining the troubleshooting I did to figure that out. I believe Calico to be implemented correctly, and that’s what I’ll describe in this post.

1. Index: busybox 060stable 100stable 100stable10817 110stable 111stable 112stable 113stable 114stable 115stable 116stable 117stable 118stable 119stable 11stable 120stable 121stable 122stable 123stable 124stable 125stable 126stable 127stable 128stable 129stable 130stable 131stable 132stable 1.
2. Sizes of busybox-1.21.1 and busybox-1.22.0 (with equivalent config, static uclibc build): text data bss dec hex filename 891522 497 7584 899603 dba13 busybox.
3. The command asks Kubernetes to run the command “sh”, enabling the interactive mode -it (so you can attach your terminal) in a new container named busybox using a specific image yauritux/busybox-curl that comes with curl preinstalled. This gives you a terminal running inside the cluster, which will have access to internal addresses like that.

Playing with Busybox. Now that we have everything setup, it's time to get our hands dirty. In this section, we are going to run a Busybox container on our system and get a taste of the docker run command. We use the 9200 port to send a cURL request to the container. $ curl 0.0.0.0:9200 'name': 'ijJDAOm'. BusyBox-Commands. Daily updated index of all busybox commands found scanning Firmware-Probes.Last update: 2021-04-23 04:36 GMT. The label (bbcmd) in the Command column shows there are other objects in this wiki using this name. The Mod column shows the amount of models using the respective command. Click the column header to sort by this number.

But, let’s start with Services. We’ve used Services a couple of times before, but let’s cover the topic a little more in depth now.

Understand Services

Kubernetes Busybox Curl

A service within kubernetes is a way to expose applications. This can either be exposing them within the cluster or to the outside world. A service name will also act as a DNS record.

So why would we need services? Why not just send traffic straight to our pods? There’s a couple of reasons you don’t want to do that: first and foremost, pods are ephemeral, meaning pods can dynamically be rescheduled on new hosts, or could even be deleted and recreated when you update a deployment. A second reason is that – depending on your networking model – your pods might only be reachable within the cluster. The default networking in Kubernetes is kubenet, which is an overlay on top of a physical network. This means, outside actors cannot reach your pods.

Enter services with a solution. A service acts as a network abstraction on top of your pods. A service is both a DNS record and an IP address; and has a port assigned to it. When you communicate to a service, you communicate to the service IP on the service port, which will be translated to a pod (load balanced) and the ports actual port.

There are 4 types of services:

• ClusterIP: exposes your service on an IP that is available within the cluster.
• NodePort: this makes a port on each nodes IP address translate those connections to your service.
• LoadBalancer: this will manage an external load balancer (typically a cloud provider’s load balancer). This will (in the backend) create a clusterIP and a NodePort as well.
• ExternalName: this maps the service name to an CNAME.

Crouzet automatismes sas driver download for windows. Note that there are 3 ports in play end the end:

• Port: The port the service will be listening on;
• NodePort: A port on each node that translates connections to your service;
• TargetPort: The port your pods are listening on.

Now that we’ve done this, let’s play around with services a bit.

Let’s start off with a simple nginx deployment:

Busybox Docker

As usual, we can create this via kubectl create -f nginx-deploy.yaml

Let’s now create a ClusterIP service to connect to our nginx.

Once created, we can see our service:

And from within the cluster, we should be able to connect to our service:

But we won’t be able to connect to this from the outside. For this, we’ll create a new service with the type Load Balancer:

We can also create this service, which will take a bit longer as an external load balancer will need to be created:

Now we should be able to connect to our service on that IP, right from our web browser:

Demonstrate basic understanding of NetworkPolicies

By default, all traffic in a kubernetes cluster can flow unrestricted. Even pods in different namespaces can communicate with each other. NetworkPolicies allow you restrict traffic to only the traffic flows you actually want to allow. NetworkPolicies work on a allow-list, meaning that once a NetworkPolicy is applied to a pod all traffic is denied by default and only allowed traffic will flow.

Within a NetworkPolicy you define which traffic can flow from a certain source to a certain destination. Sources and destinations can either be IP addresses or ranges or can be pods within your cluster. You define which pods with the right selectors.

If you are planning – like me – to run this example on an Azure Kubernetes Cluster, make sure your cluster is enabled for Network Policies. They aren’t by default. You’ll want to add the --networkpolicy calico flag to your az aks create. It cannot be applied after a cluster has already been created.

Let’s build a simple example to demonstrate how NetworkPolicies work. We’ll create 4 pods within the same namespace. 2 busybox-curl pods, 1 with a trusted label, 1 without a trusted label and 2 nginx web servers, both with label app=web, and 1 with label env=dev and the other with label env=prod.

Let’s create a new namespace for our networking work, and set it as the default for our kubectl:

By now I expect you’d be able to create the YAML for these pods, so try to write this yourself before checking mine:

We can create this with kubectl create -f pods.yaml. Let’s get the IPs of our Nginx servers – and try if we can connect to both from both our busyboxes:

If your results are the same as mine, all traffic flows, from both busyboxes to both nginx servers.

Let’s now define our first NetworkPolicy, which will allow traffic only from busyboxes with the label trusted=true. This will look like this:

We can deploy this policy with kubectl create -f policy1.yaml. Creating this policy has no impact on the running pods (they remain up and running) but will impact network network almost instantly. Let’s test it out:

Let’s now also deploy our second policy, which will limit egress traffic from our trusted busybox, only to the dev environment. This policy looks like this:

Let’s create this policy as well, and see what the effect is. kubectl create -f policy2.yaml

That was cool. Let’s make our experiment a little more complex by adding two new nginx pods: one with the label env=dev (but no longer the app label, so policy1 doesn’t apply) – and one with the label trusted=yes. And then it’ll be our job to figure out which traffic flows are allowed in our experiment, those new arrows are the purple arrows in our drawing below:

The following YAML will create our new pods:

Let’s start with the two arrows going from busybox-curl-1:

Let’s do the same for busybox-curl-2:

This will make our picture look like this:

Conclusion of the working of NetworkPolicy (using Calico)

Busybox Container

We’ve deployed a couple of NetworkPolicies now, and I hope you have the same understanding as I do:

• If there are no policies, all traffic is allowed.
• If there is only a ingress policy, traffic from the sources mentioned in the ingress policy is allowed.
• If there is only a egress policy, traffic from to the destinations mentioned in the egress policy is allowed.
• If there is a combination of ingress and egress policies, only traffic allowed by both will be allowed.

Conclusion

In this part we repeated some of our work with Services on which we touched earlier. We also took a look into NetworkPolicies. For those of you interested in the ramblings of a mad man looking for answers, I have a seperate post explaining some of the troubleshooting I went through to figure out something was broken was Azure NetworkPolicies.

• PDF Link: cheatsheet-kubernetes-A4.pdf, Category: Cloud
• Blog URL: https://cheatsheet.dennyzhang.com/cheatsheet-kubernetes-A4
• Related posts: Kubectl CheatSheet, Kubernetes Yaml, #denny-cheatsheets

File me Issues or star this repo.

1.1 Common Commands

1.2 Check Performance

1.3 Resources Deletion

1.4 Log & Conf Files

1.5 Pod

1.6 Label & Annontation

1.7 Deployment & Scale

Busybox Curling Iron

1.8 Quota & Limits & Resource

1.9 Service

1.10 Secrets

1.11 StatefulSet

1.12 Volumes & Volume Claims

1.13 Events & Metrics

1.14 Node Maintenance

1.15 Namespace & Security

1.16 Network

1.17 Patch

1.18 Extenstions

1.19 Components & Services

1.19.1 Services on Master Nodes

1.19.2 Services on Worker Nodes

Busybox Curly

Busybox Curl Not Found

1.19.3 Addons: pods and services that implement cluster features

1.19.4 Tools

1.20 More Resources

License: Code is licensed under MIT License.