The abstraction would mean that

The abstraction would mean that the containers could ephemeral all they like and the rest of the cluster wouldnt care. More or less. brk(NULL) = 0xc01000 Error: required flag(s) "replicas" not set For instance, I recently built an app that needed to send some metrics to a Prometheus server. Find more information at: https://kubernetes.io/docs/reference/kubectl/overview/ With that out of the way, the output of our kubectl explains deployment mentions 2 other things: Pods and ReplicaSets. On your machine. Containers provide namespace isolation i.e. Now that we have the virtual environment set up, we can install flask in it without polluting our global Python installation.

This is also used to make user extensions for Kubernetes, which is out of scope for this book. Examples: cat pod.json | kubectl create -f -.. The examples in this book will use Flask.

expose Take a replication controller, service, deployment or pod and expose it as a new Kubernetes Service Wait, what? A virtual environment is nothing but a copy of all the files that are needed to run Python applications. Instead of the one that is running on your machine, outside the VM. This might still feel very abstract. Did I tell you that we will be using Python 3 in this book? df20fa9351a1: Pull complete During the initialization of the web app, we also create some new objects. Until it doesnt. Newer tools, including Kubernetes, are declarative. edit Edit a resource on the server It seems we are looking for 2 at this moment. The advent of DevOps has meant many things to many people but for me, it means no cake. Collecting itsdangerous==1.1.0 In this case, it is common to tag the image as staging when it is published. Success! COPY hello.py / Someone would set out to do it and 3 days later, everyone will get a slice of cake. Lets move on to the next interesting bit in our kubectl tour: We just ran our thing on a cluster and now we are querying the cluster and its telling us the nuts and bolts of how its running our thing. When you do choose to scale your cluster, Kubernetes will automatically create new containers on the new nodes and divert traffic to them. Removing intermediate container 9527747772b7, REPOSITORY TAG IMAGE ID CREATED SIZE, python alpine 872c3118ec53 2 days ago 42.7MB, REPOSITORY TAG IMAGE ID CREATED SIZE

We will be using Flask. So firstly, lets create a virtual environment for our little Hello World project. pod (po), service (svc), replicationcontroller (rc), deployment (deploy), replicaset (rs) Created wheel for MarkupSafe: filename=MarkupSafe-1.1.1-py3-none-any.whl size=12629 sha256=7020159b31f20b65caec66087f40ff4a4e235219689d8235bbbc8b5187ef717d The Kubernetes service acts as a load balancer, and we dont control which one. A Selector is a string that selects a set of resources in a Kubernetes cluster based on their labels. Examples: kubectl patch node k8s-node-1 -p '{"spec":{"unschedulable":true}}', kubectl patch -f node.json -p '{"spec":{"unschedulable":true}}', 's image; spec.containers[*].name is required because it', kubectl patch pod valid-pod -p '{"spec":{"containers":[{"name":"kubernetes-serve-hostname","image":"new image"}]}}'. Lets see if kubectl does a better job of explaining that these are: Not bad but perhaps I can expand on this with an example. Let me explain. I can explain what a deployment is if we can take a step back and let kubectl help us explore the size and shape of what we have just done here. One more thing: All the commands produce layers but except for FROM, COPY and RUN, the layers are intermediate. We wanted all the good things - docker for reproducible and distributable artefacts, CI/CD and a high release cadence without locking down 50% of our engineering resources. In the template, you find the same structure as the deployment, but apiVersion and kind are implied in this case. -rwxr-xr-x 1 alixedi staff 281 Jul 31 13:01 easy_install-3.7 Nothing new there, unless you are the best developer in the world! Who is excited? convert Convert config files between different API versions Example resource specifications include: We have - by now - figured out: How to deploy our application to a Kubernetes cluster. Its a repository. close(3) = 0

-rwxr-xr-x 1 alixedi staff 281 Jul 31 13:01 easy_install If you are having problems, give us a shout. Like most cool ideas, the sandbox idea increases in awesomeness if we turn it up to 10. create Create a resource from a file or from stdin. Successfully installed Jinja2-2.11.2 MarkupSafe-1.1.1 Werkzeug-1.0.1 click-7.1.2 flask-1.1.2 itsdangerous-1.1.0. Our problem - like every other startup was optimizing the infrastructure costs to try and get the maximum bang for our buck. selector Set the selector on a resource image"}]', $ kubectl create deployment webconsole --image webconsole:v1 \, HTTP response headers: HTTPHeaderDict({'Content-Type': 'application/json', 'X-Content-Type-Options': 'nosniff', 'Date': 'Mon, 25 Jan 2021 11:29:21 GMT', 'Content-Length': '366'}), "/usr/local/lib/python3.9/site-packages/kubernetes/client/api/batch_v1_api.py", "/usr/local/lib/python3.9/site-packages/kubernetes/client/api_client.py", "/usr/local/lib/python3.9/site-packages/kubernetes/client/rest.py", "/home/paul/anaconda3/envs/tut-ex/lib/python3.9/site-packages/kubernetes/config/incluster_config.py", 'http://172.17.0.2:32535/api/paul/start/', by tinkering instead of looking at block diagrams, by doing instead of listening to how its done, Demonstrate Kubernetes to their colleagues, Manage your deployment e.g. Advanced Commands: Good. The thing with web applications - like all applications - is that they need to be chucked around fairly often. For those who do not know, Flask is a minimal web framework for Python.

Not because we had a million teams and services were the only way to stop them from treading on toes. I think you realized why this is happening.

Namespace: default Until now. Lets start by exploring scale. and try to push out a new release. Installing flask in a venv would mean that it is not available globally: We wrote ourselves an exciting little application in Flask. A deployment or You should change the base image from. DESCRIPTION: You would need some way to differentiate hello 1.0 from hello 2.0. drwxr-xr-x 9 alixedi staff 288B Jul 31 13:09 Jinja2-2.11.2.dist-info I dont know about you but I the examples. You can also assign multiple tags to an image. Finally, we were 2 engineers in total. Lets deploy all this YAML, and cleanup the manually created job. Use a production WSGI server instead. Here we are then. Twice. run Run a particular image on the cluster. Lets YAML : This role gives us access to two API groups on lines 7 and 13: batch and core. As always with development, having a proof of concept is nothing compared to creating something you can run on production. Turns out we could.

To finish this long wall of YAML manifests, I should prove we have a working application.

dr-xr-xr-x 12 root root 0 Aug 7 13:16 sys created by clients and scheduled onto hosts. Examples: on port 8000. Name: webconsole clusterrole Create a ClusterRole. webconsole-5b559bf485 1 1 1 42m, Basic Commands (Intermediate): 78538f72d6a9: Pull complete We think that this would be enough to learn Kubernetes. As a user, we will generally deal with Deployments and Pods instead of ReplicaSets. 50644c29ef5a: Waiting, FROM python:alpine Each of those objects can be serialized to a document in either JSON or YAML. Mmh, deployment , isnt that what we are trying to do? What exactly is distribute anyway? Sometimes. We are running Minikube - which runs a Kubernetes cluster on our machine. -rw-r--r-- 1 alixedi staff 2452 Jul 31 13:01 activate.fish

As we established earlier, a service is an abstraction that exposes a deployment to the rest of the world. In case you are not familiar with Python or Flask, we will walk you through the code. Isnt that convenient ? To check if our virtual environment is doing what it said on the tin. Explain seems to suggest documentation of some kind. * Debug mode: off A better way would be to name the images hello and tag them v1 and v2 respectively. kustomize Build a kustomization target from a directory or a remote url. mmap(NULL, 17010, PROT_READ, MAP_PRIVATE, 3, 0) = 0x7f8719d60000 the selector that determines which pods will answer requests sent through Possibly, promulgating an engineering culture where the respective teams oversee particular features of the broader application from conception, design, development, all the way into production. The toast at the bottom of the sandwich takes whatever the function returns and passes it back to the client that hit the root of our web application. Lets use another kubectl subcommand to help us out here: It seems our deployment has something called a selector. You might not find a lot of paragraphs either. serviceaccount Update ServiceAccount of a resource Back to Dockerfiles. Lets see if it works. To cut a long story short, to do this, I needed to pair each container running my app with one running StatsD exporter. We have something reproducible and not a . But also I realise that we havent run the damned thing yet! 3e7ef1bb9eba: Pull complete port is specified via --port and the exposed resource has multiple ports, all will be re-used by the Lets take a look at those files, and see what the deal is. Service selector label resource blah blah blah blah.. As it turns out, there are the 2 types of services in Kubernetes that you should be aware of at this instant in time: The attentive reader might ask at this point: Why do we need a service for exposing our application inside the cluster?. Rest of the world for your web application would mean the internet. If it happens to land on the wrong one, our code wont execute ! It should be pretty simple and easy to follow. Motivation leads to action. drwxr-xr-x 8 alixedi staff 256B Jul 31 13:09 Werkzeug-1.0.1.dist-info, execve("/home/alixedi/k8s/bin/python", ["python"], 0x7ffee2a890b0 /* 24 vars */) = 0 ), lets deploy this together and try it out: Aargh, I missed something, again It still doesnt work ! We will introduce you to everything you need to run most applications on Kubernetes, and even use some of its advanced features.

You can move a bunch of things in this tedious command line into the Dockerfile. Containers provide file system isolation. Kubernetes always tries to rely on the actual state, not the state it saved in memory or on disk. Meh. As a thank you, everyone, who subscribes will get a 50% discount on the book , drwxr-xr-x 6 alixedi staff 192B Jul 31 13:01 . Just replace hello.py with webconsole.py: A little demonstration on how to use it from a python script (pip install a handy package called requests first): Of course, this is far too simple. Remember our setup? Kubernetes helped us do all of that and it can help you too. Dont you it when the API is this good? dr-xr-xr-x 144 root root 0 Aug 7 13:16 proc Lets check the error in a more readable form. Kubectl set looks very limiting. Status: Downloaded newer image for python:alpine, Step 2/3 : COPY hello.py requirements.txt /, Step 3/3 : RUN pip install -r requirements.txt, Collecting click==7.1.2 In the last chapter, we learned how to build an image. Node: minikube/192.168.64.2 Also, take weird Segways. Find more information at: https://kubernetes.io/docs/reference/kubectl/overview/ In keeping with this principle, we would like to fiddle with Kubernetes. A process running in a container cannot access the file system outside of the container. Remember: you might want to use the docker daemon which is running inside minikube. Note that if no A docker image is a stack of these layers. Maybe to 8. MarkupSafe==1.1.1 Why is it cool? Building wheel for MarkupSafe (setup.py): started Show me or it didnt happen. Type "help", "copyright", "credits" or "license" for more information. So lets talk about why you should be happy about it before you burn the book (and your laptop with it ebooks are not so fun to light on fire). kubectl set SUBCOMMAND [options]. " We hope that this investment will pay dividends in your understanding and confidence when it comes to applying things that you learn here to your projects. They might have documented stuff (which got out of date) and used handy tools (which would run a command on several servers). This will push the hello:v1 image to dockerhub. Successfully built MarkupSafe Possible resources include (case insensitive): Following this, it might be prudent to point your Docker CLI to the docker daemon that is running inside the VM. Now to activate this virtual environment, we have - the activate script. kubectl - the CLI tool for Kubernetes lets us do just that. So lets check set and patch. The only change is line 20, we just added serviceAccount: consolehub , to make clear we want to use the Service account. There are also tools to help you, we briefly touch on that in chapter <>. Or maybe we missed something else Lets start a python interpreter on our local machine (Make sure you have the above python packages installed! new service. We have a cluster. Hang on a minute, we are moving straight to requirements.txt. LOL. [Clang 11.0.3 (clang-1103.0.32.62)] on darwin patch Update field(s) of a resource using strategic merge patch Do not use it in a production deployment. A little bit of history. On the server, you would need to reproduce the environment that your web application needs to run. We started with a little Hello World application in Python and introduced Pythons virtual environment to make our application reproducible and distributable (I am surprised this is a word). Successfully installed Flask-1.1.2 Jinja2-2.11.2 MarkupSafe-1.1.1 Werkzeug-1.0.1 click-7.1.2 itsdangerous-1.1.0 Alright, I am now satisfied that we have touched most of the bits in docker that matter. Lets demonstrate this. We need to create a user which gives us enough access to do the operations we need. -P, --publish-all Publish all exposed ports to random ports, "FLASK_APP=hello.py flask run -h 0.0.0.0", FROM python:alpine I think I have an idea on how to do example #3 for our thing.

We chose to build an interactive Python web console - A webpage that lets users type and run arbitrary Python code. I promise. resource it exposes. We wanted to be able to scale up when it was time to make money and scale down when we didnt have active customers. I do. Lets break it down: The command: kubectl create deployment webconsole just says we want to create a deployment with the name webconsole, we then provide some options like the image and a port number. Not to mention: you are allowing anyone to run any code on your servers! You got 2 new junior engineers on your team.

You can use the last Dockerfile for this. Enough talk.

So far we only used the Kubernetes API with kubectl, and minikube automatically configures kubectl to have superuser permissions . webconsole-5b559bf485-2zkt5 1/1 Running 0 4s Jinja2==2.11.2 If you like this, you might be pleased to know that we are working on a book that follows the same principles as this tutorial: In addition to the material covered in this tutorial, the book will also cover: If you are interested in the book, please let us know by putting your email in the form below and hitting I want the book. Finally, how can I inspect these layers? Also, when you are building a new image, Docker is smart enough to only download layers that are not present in the local file system. DESCRIPTION: Deleting and recreating it doesnt feel right, who would bring down their application to update it? [Clang 11.0.0 (clang-1100.0.33.8)] on darwin drwxr-xr-x 2 alixedi staff 64B Jul 31 13:01 include Everything in Kubernetes from the pod running your software, a deployment managing those pods (recreate crashed and other nice features), to exposing something on the network (a service) is an object. This is where repositories come in.

We should now - by all accounts - have a way of pointing to our application from outside the cluster.

Werkzeug==1.0.1, # Install required packages into the venv, total 72 . -rw-r--r-- 1 root root 95 Aug 7 09:30 requirements.txt Spec describes the actual object and is different for every type. cronjob Create a cronjob with the specified name. A very basic Dockerfile for our application would look like the following: 1 - Every docker container has a base image (More on images in the following paras). In line 14 we initialize the Kubernetes API and load the configuration from the cluster. Lets have a look at the spec of the deployment: replicas declares how many pods you want to run, the selector declares how to find your already pods, the strategy how to update when you change something (like the image), and the template is the template (that explains a lot!) Python venv as the analogy for Docker died as soon as we moved from the What (isolation) to the How (API). __name__ in Python is bound to the name of the current module which is based on the file name. -p, --publish list Publish a container's port(s) to the host create Create a resource from a file or from stdin. It looks like this: Making an interactive Python web console might sound complicated but we will be doing it one step at a time and we get a nice helping hand from Python: In less than 10 lines of code, we have something that behaves like a primitive Python command line: We can easily combine this with our Docker hello world example and we have a (multi-user) interactive web console. Inside a VM. Perhaps its time to dive back into the kubectl and see what else we have at our hand . WARNING: This is a development server. This abstraction is called Service Discovery. Every time someone in your team adds a little feature to it, you might want to run some tests using e.g. They need to quickly and easily be able to run your massively complex Hello World application on their local machine to build new features and get you that VC . Luckily a lot of that is kind of redundant or even not relevant. Your CTO - in his/her infinite wisdom - have chosen to use Kubernetes to orchestrate all those microservices. It will happily distribute the traffic to ensure a stable deployment. The most popular one no less. If a pod misbehaves, and Kubernetes decided to kill it for everyones safety, the pod wont be relocated, but the deployment will create a new pod. Back to the bit where we were trying to expose our application running inside a Kubernetes cluster to the internet. As this is just a tutorial we are not going in-depth, but Kubernetes has something called RBAC: Role-based access control. We could run it now but I am inclined to shamelessly double down on the BS and introduce one more concept before that. Installing Minikube is about following this excellent guide. RUN pip install -r requirements.txt, IMAGE CREATED CREATED BY SIZE COMMENT We can use these labels later to find back our running webconsole. Orchestrate is a word that is used often to describe Kubernetes. hello:v1 . KIND: ReplicaSet you ask.

Also if no labels are specified, the new service will re-use the labels from the VERSION: v1 At least from a utilitarian perspective. Lets answer these questions by running the following bit of command line: Except for next time, we could bundle up the naming and tagging in the build command itself: Now that we know HOW to name and tag our images, its probably useful to understand WHY. Its time we smooth this out. We have Minikube. Namespace: default Like we said the code in the decorator sandwiches the code in our function. This is what containers do. You wrote scripts to tell the server how you wanted to change something, it might have checked for a condition to ensure your cloud also run the script on a clean server. -rwxr-xr-x 1 alixedi staff 263 Jul 31 13:01 pip3

The clever writer would then move on swiftly to Docker concepts and hope that the analogy with Python venv has caused more good than harm. Lets continue, and try to create a job: Thats a lot better! Given that this tutorial started as a workshop, it is quite hands-on. Now to run tests on your application, GitHub actions would need to be able to easily install it - along with all its dependencies no? What happened to be able to create a virtual environment by running: Followed by activating the virtual environment and installing a bunch of packages by: Docker has its own opinions on sandboxes, how they should be built and how processes should be run inside them. The first thing you could do is to run your container with a shell and faff about: I would also invite you at this point to summon the help and find out what interactive and tty means: Nice innit? [options]. Virtual environments are cool because they let you install packages on per-project bases without polluting your global Python installation. Given that this is now a write-up, it might take you longer. The first thing we need to do is to write the Docker equivalent of our requirements.txt file i.e.

We wont build the front end, just the JSON API which would power it. selector for that resource as the selector for a new service on the specified port. For instance, imagine you test your application in a staging environment before promoting it to production. resources Update resource requests/limits on objects with pod templates digression into Python nitty-gritty. Before I move to containers and specifically Docker containers, I want to press home my advantage and introduce one more little magic trick in pip. ^ Collecting Jinja2==2.11.2 As soon as the credits ran out, there was a possibility that we would move shop for cost efficiency. Lets refer to the help and pay close attention to the Usage: You will notice the switch that specifies the service type. Minikube will let you fiddle away at that Kubernetes cluster without having to pull out your wallet and spend your hard-earned AWS credits. Break things. Step 1/3 : FROM python:alpine We just built one. A repository is a central store for your images. a file that lay out what would go into our container. '--filename=rsrc.json', See 'kubectl expose -h' for help and examples. The message in the response is talking about a user which doesnt have access to job.batch. So far we can only create a deployment in Kubernetes, delete it, or scale it. Type "help", "copyright", "credits" or "license" for more information. create Create a resource from a file or from stdin. delete Delete resources by filenames, stdin, resources and names, or by resources and Downloading MarkupSafe-1.1.1.tar.gz (19 kB) Not because of resume-driven development. For starters, we should just type kubectl in our terminal and see what that goes: Lots of interesting things under the ellipses but honestly, do we feel like reading beyond create? This is fine. The job is given a name at line 21, and attach some labels to it at line 24. We have also managed to figure out how to scale our application. Collecting MarkupSafe==1.1.1 network, process IDs, hostnames, users etc. configmap Create a configmap from a local file, directory or literal value Dont worry if you dont, we will still explain it. Digest: sha256:1edaccf11f061da18842e3cb7bb14d9f7336b6b2a24248219ab5c363b8454336 You can request the logs from any pod with kubectl: We got a 403 Forbidden from the Kubernetes API. The code needs to be able to create (11) jobs and list (17) pods. I feel that my main job, as an author, is to get the readers excited about something because lets face it: Excitement leads to motivation. Anything or anyone who wants to run our web application should be able to do so by following some simple steps: You can put these steps in a console script and it would work beautifully. Tear them apart to see how they work. replica set will be exposed as a service only if its selector is convertible to a selector that You can do it like so: P.S. Downloading Jinja2-2.11.2-py2.py3-none-any.whl (125 kB)

Containers provide a sandbox for your process to run in. SyntaxError: invalid syntax, ModuleNotFoundError: No module named 'flask', * Serving Flask app "hello.py" The function finishes at line 29 by calling the Kubernetes API to create the job. webconsole-5b559bf485-fvb6c 0/1 Terminating 0 117s Lets nail down what that means before we move on with the rest of our story. Hold that thought. One way to do it would be to name the images hello1 and hello2 respectively. Using a Hello World application was a bit of a necessity because we wanted complete attention to the container and not what was running inside it. Basic Commands (Intermediate): How about you work at a startup that is trying to find a product-market fit by deploying e.g. Look up the watch switch. Without any obvious exceptions, the most awesome thing you could do with a Dockerfile is to use it to produce a Docker image. Before you get started, make sure you have installed the following on your system: Lets start with a very simple Hello World API in Python. Some of these opinions are informed by the difference in nature between a docker sandbox to a Python venv sandbox. But what about MY image? Downloading itsdangerous-1.1.0-py2.py3-none-any.whl (16 kB) We were on startup credits. KIND: Pod

--health-retries int Consecutive failures needed to report unhealthy Instead of sending this manifest as is, we treat it as a template! Do not use it in a production deployment. This is called imperative for the nerds under us. Why? A little reminder of what a Python virtual environment is. We also said that the toast at the top of our sandwich essentially passes control to our function whenever the root of our web application is hit. We found a bug, and we know how to update our application in Kubernetes . We have figured out a way to expose our service to the world outside the cluster but that world is just a VM. But even with the shitty product, they would not want the embarrassment of being brought down by a TechCrunch article. A set of containers that are running a particular microservice need a PO box - A layer of abstraction over the (IP) addresses of individual containers.

We need a better user. get Display one or many resources KIND: Service In these API groups, we request access to the resources we use: jobs (9) and pods (15). I will come back to this shortly. So Big Corp has launched this awesome new product.

We are using the python base image with the tag alpine. This is just for us to cheat, and simplify the code . You tell the server, or with Kubernetes, a cluster instead, what things should look like.

Each layer can be re-used by an unlimited number of images. 's image using a json patch with positional arrays. Lets try and faff about as promised: Now we just want to lift whatever we did in that container to get our little app running.

run=webconsole, Usage: I have worked at companies where a release was like a ceremony.

NAME SHORTNAMES APIGROUP NAMESPACED KIND And this is why we should probably use the apply command, you just send the same document with (minor) changes over, and Kubernetes will make it happen. Not enough CLI tools have them IMO. We will revisit this pretty soon. Start Time: Fri, 28 Aug 2020 09:02:22 +0100 I have put newlines in the snippet above to distinguish the various steps that were needed for building our docker image. It also comes with a bunch of nice-to-haves which makes it easy for beginners. access("/etc/ld.so.nohwcap", F_OK) = -1 ENOENT (No such file or directory) ReplicaSet ensures that a specified number of pod replicas are running at Looks up a deployment, service, replica set, replication controller or pod by name and uses the We will come back to it when we talk about Kubernetes. webconsole 1/1 1 1 9s, NAME READY STATUS RESTARTS AGE env Update environment variables on a pod template Inside that VM is a Kubernetes cluster. And thats all the code. Jobs will automatically create a new pod, depending on some conditions, and the normal restarting will just mess that up. But we are still in a halfway house here. Generally, for web applications, this would mean putting them on a server. It is the thing that you can scale up or down. Lets ask it about deployments, shall we?

We hope you enjoyed this whirlwind tour of modern DevOps just as much as we enjoyed writing it. Collecting Werkzeug==1.0.1

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The abstraction would mean that