How to get to operator

Thomas Suedbroecker’s Blog

I want to share my experience in the cloud development area.

Develop a simple operator to deploy a web application using the GO Operator SDK

This blog post is a bigger cheat sheet about how to start with an operator implementation with the GO Operator SDK and also contains some details how to define Kubernetes deployments, secrets, and services.

That blog post does reference an example GitHub project called Example Tenancy Frontend Operator. This project contains the source code for the example operator.

That operator has only one simple objective:

Deploy the example frontend application of the Open-Source Multi-Cloud Asset to build SaaS project to a minikube instance on the local computer.

Therefor the Example Tenancy Frontend Operator creates following Kubernetes resources:

The source code of the example frontend application is available in the open sourced GitHub project multi-tenancy-frontend.

Again, just get the frontend application running on minikube using an operator!

The source code of the frontend application is available in the open sourced Multi Tenancy Frontend GitHub project. In case if you are interested in details of the deployed application, just take a look into that source code.

Remember: As I said, this is only a bigger cheat sheet and not a workshop with detailed steps of the developed example operator and the related explanations.

If you want to reproduce some of the steps, you should ensure you have installed the Operator SDK, GO, Docker and minikube. To get the source code you just need to clone the project Example Tenancy Frontend Operator to your local machine.

That very simplified diagram shows what the local running example frontend operator basically does:

I did a live stream related to this blog post. In that live stream I deployed the frontend application to a free IBM Cloud Kubernetes cluster. Extended PDF of the slides used in the live stream.

These are the sections of the blog post:

If you only want to run the example «Frontend Operator» you can skip this section and start with “2 Get a basic understanding of some parts in the operator implementation“.

1. Generate an own Operator API using the GO SDK

That section contains steps you can follow on your computer to create your own Operator API, here you should get a basic understanding of the folder structure and the created files.

The created Operator API project is just a temporary project which we can delete.
later in section “2 Get a basic understanding of some parts in the operator implementation“ we will use the existing developed Example Tenancy Frontend Operator and clone it to our local computer.

Step 1: Create a project folder called frontendOperator

That folder name will later be reused in the PROJECT file as the project name.

Step 2: Init a new operator project

This is only an output and you don’t need execute any of the written example commands.

Step 3: Create a new Operator API

This is only an output and don’t execute any of the written example commands.

Step 4: Install missing components or version, if needed

This is related to the definition in your go.mod file. Your local installation must fulfil the required packages defined here.

2. Get a basic understanding of some parts in the operator implementation with the GO SDK

In that section we will clone the existing project to your local computer. And then we have a walk through to different topics of the implementation, just by viewing existing example code.

We will not work with the project, which was created before!

The before created project was just to ensure we get a basic understanding how the project and API creation works with the Operator SDK and which files and folders were created.

2.1. Let’s start with the setup of the example on the local machine

In these steps we setup the existing example on the local machine.

Step 1: Create a new folder on you machine:

Step 2: Clone the operator code into the “example” folder:

Step 3: Navigate to the frontendOperator folder of the cloned project

Step 4: Add the folder frontendOperator to your Visual Studio Code workspace

If you just want to run the frontendOperator you can skip this section and move on with 3. Run the operator locally and verify, if the frontend is deployed and accessible on minikube.

2.2 Let’s understand the existing code of the project.

2.2.1 How to define content for a custom resource definition in the frontendOperator/api/v1alpha1/tenancyfrontend_type.go file?

In this file we define entries of our custom resource definition (CRD) and the file will be used later, when we will execute the two commands make generate and make manifests which will create the CRD definition for our operator.

As you see these function contains only two values, which we will use in the example operator to create the frontend application instance.

This is just an example entry: Size int32 json:”size”“

2.2.2 Understand a bit the controller

The tenancyfrontend_controller.go file contains the controller loop implementation.

In that tenancyfrontend_controller.go file is a reconcile function, that is responsible to ensure that the desired state for our operator will be achieved, that means all the given custom resource definitions for instances we will be deployed to minikube and frontend application will be deployed.

At the beginning of that file we find imports of existing GO packages we need to interact with Kubernetes.

These are example links to some GO Kubernetes packages:

2.2.3 Remember the basics of the reconcile function

The reconcile function is responsible to ensure that the desired state of our operator will be achieved, that means for all the given custom resource definition instances ( yaml’s which have been applied to minikube) the reconcile needs to verify, if there are all frontend applications deployed.

These are the major steps of the example code extract.

Note: This is just a simpler and older extraction of the example code. You don’t need to change the code you have cloned from the repository.

We also need to ensure that this function has the access rights to modify the Kubernetes resources on minikube. Therefor following two lines added above the reconcile function.

2.2.4 Ensure that a container image is available for the deployment

We need to ensure that a container image for our frontend is available in a public container registry (just for simplification). In the current situation we can use a container image on quay.io I created.

If you want to create an own container image for the frontend, you can clone the code from the Multi Tenancy Frontend GitHub project and push a container to a public registry.

2.3 How to define the deployments?

2.3.1 UNDERSTAND THE ACTUAL DEPLOYMENT OF THE FRONTEND APPLICATION

Before we start to implement the deploymentForTenancyFrontend function, we need to verify and understand what the structure of the existing frontend application deployment does. We can do this by visiting with the given Kubernetes deployment in a yaml format, in this case you can use the deployment.yaml given in the Multi Tenancy Frontend GitHub project for the source code of the frontend.

Here are some of the important values:

2.3.2 UNDERSTAND THE IMPLEMENTATION OF THE DEPLOYMENT DEFINITION

Later on, we will define the liveness and readiness probes therefor, we define an execution command we will use later. Here you see how a GO slice is used to define the command for the liveness and readiness probes, we have seen in the yaml above.

An important part of the deployment implementation is the definition of the environment variables which are described by using secrets or simply values. Also the implementations of the liveness and readiness probe are interesting.

These are the imported package for Kubernetes, which are used in the source code:

The following GO source code shows the deployment definition implementation, for the deployment above.

You see that the specification of the custom resource definitions are used in that function.

That deployment will be deployed in the reconcile function with the Create function, provided by the reconciler instance. For more details visit the documentation.

2.4 Services and secrets definitions

The frontend application normally needs a backend service and a configured IBM Cloud AppID service to run, but we will not provide that information.

2.4.1 Understand the service definition for NodePort and ClusterIP

First understand the existing Kubernetes service definitions formats in the given yaml you find in the Multi Tenancy Frontend GitHub source code project.

2.4.2 Implement the NodePort and ClusterIP service definitions

The services and secrets will be deployed in the reconcile function with the Get function provided by the reconciler instance. For more details visit the documentation.

3. Run the operator locally and verify, if the frontend is deployed and accessible on minikube

If you want to run the example operator on your local machine you need to follow the next steps.

3.1 Recreate the needed operator manifests

Just to ensure all your environment is working.

STEP 1: ENSURE APPLICATION IS CREATED

STEP 2: CREATE THE MANIFESTS ALL NEEDED YAMLS

3.2 Run the operator on minikube

STEP 1: START DOCKER DESKTOP

STEP 2: START MINIKUBE

STEP 3: OPEN THE MINIKUBE DASHBOARD

STEP 4: RUN THE OPERATOR LOCALLY

This will run the operator locally and connects to the minikube with have running on the local machine.

That means the operator isn’t installed at minikube, but does observe the Kubernetes API of minikube. With that in mind, we will later create a frontend application instance in minikube by deploying a CRD with our operator.

In the output, we see that the operator is connected to minikube and observes the Kubernetes API.

Inside the Kubernetes dashboard we see we don’t have anything deployed with our operator until now to minikube, as you see in the image below.

STEP 5: DEPLOY A CUSTOMER RESOURCE TO CREATE A FRONTEND APPLICATION INSTANCE

Open a new terminal and apply the example definition of our example CRD.
Note: Ensure you are in the frontendOperator project folder.

STEP 6: VERIFY THE OUTPUT in the TERMINAL WHERE THE OPERATOR runs

Now we see an example of a deployed secret appid.client-id-frontend in minikube.

Target secret appid.client-id-frontend exists shows that the secret is deployed.

In the following gif we see the created resources for the frontend web application we created with our operator. REMEMBER: The operator only runs only locally and doesn’t run in minikube.

STEP 7: ACCESS THE EXAMPLE APPLICATION

Open a new terminal.

a) Try to use NodePort

That will not work with minikube on our local computer, but we can verify the needed steps.

Step 1: Get the node port of the service-frontend

Step 2: Get minikube IP

Note: In case if you have running a Kubernetes Cluster on IBM Cloud.

Step 3: Open the example application in the browser

You will notice this will not work!

b) Using tunnel for minikube

The tunnel will work to access the example frontend application and we will create an additional service for the frontend application deployment, by exposing the tenancyfrontend-sample deployment.

Step 1: Create a tunnel

Step 2: Get the deployments

Open a new terminal and get the deployments.

Step 3: Expose the deployment (which creates a new service)

Step 4: Get the newly service created service

Now you can see the external IP for that service and the

Step 5: Access the example application

Open the application in your browser.

Summary

This is really a bigger cheat sheet, but it covers from my perspective very essential topics differently to the memcached example of the Operator SDK.

I hope this was useful for you and let’s see what’s next?

#operator, #go, #operatorsdk, #minikube, #kubernetes, #buildlabs4saas, #operatorlearningjourney

operator-framework/getting-started

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README.md

[DEPRECATED] Getting Started

This project is deprecated. Documentation for the Operator Framework has moved to https://operatorframework.io/

The Operator Framework (intro blog post) is an open source toolkit to manage Kubernetes native applications, called operators, in an effective, automated, and scalable way. Operators take advantage of Kubernetes’s extensibility to deliver the automation advantages of cloud services like provisioning, scaling, and backup/restore while being able to run anywhere that Kubernetes can run.

This guide shows how to build a simple memcached operator and how to manage its lifecycle from install to update to a new version. For that, we will use two center pieces of the framework:

Build an operator using the Operator SDK

The Operator SDK makes it easier to build Kubernetes native applications, a process that can require deep, application-specific operational knowledge. The SDK not only lowers that barrier, but it also helps reduce the amount of boilerplate code needed for many common management capabilities, such as metering or monitoring.

This section walks through an example of building a simple memcached operator using tools and libraries provided by the Operator SDK. This walkthrough is not exhaustive; for an in-depth explanation of these steps, see the SDK’s user guide.

Requirements: Please make sure that the Operator SDK is installed on the development machine. Additionally, the Operator Lifecycle Manager must be installed in the cluster (1.8 or above to support the apps/v1beta2 API group) before running this guide.

Create a new project

This creates the memcached-operator project.

NOTE: Learn more about the project directory structure from the SDK project layout documentation.

The main program for the operator cmd/manager/main.go initializes and runs the Manager.

The Manager can restrict the namespace that all controllers will watch for resources:

By default this will be the namespace that the operator is running in. To watch all namespaces leave the namespace option empty:

Add a new Custom Resource Definition

Define the Memcached spec and status

Modify the spec and status of the Memcached Custom Resource (CR) at pkg/apis/cache/v1alpha1/memcached_types.go :

After modifying the *_types.go file always run the following command to update the generated code for that resource type:

Also run the following command in order to automatically generate the CRDs:

You can see the changes applied in deploy/crds/cache.example.com_memcacheds_crd.yaml

Add a new Controller

Add a new Controller to the project that will watch and reconcile the Memcached resource:

For this example replace the generated Controller file pkg/controller/memcached/memcached_controller.go with the example memcached_controller.go implementation.

The example Controller executes the following reconciliation logic for each Memcached CR:

The next two subsections explain how the Controller watches resources and how the reconcile loop is triggered. Skip to the Build section to see how to build and run the operator.

Resources watched by the Controller

Inspect the Controller implementation at pkg/controller/memcached/memcached_controller.go to see how the Controller watches resources.

The first watch is for the Memcached type as the primary resource. For each Add/Update/Delete event the reconcile loop will be sent a reconcile Request (a namespace/name key) for that Memcached object:

The next watch is for Deployments but the event handler will map each event to a reconcile Request for the owner of the Deployment. Which in this case is the Memcached object for which the Deployment was created. This allows the controller to watch Deployments as a secondary resource.

For a guide on Reconcilers, Clients, and interacting with resource Events, see the Client API doc.

Build and run the operator

Before running the operator, the CRD must be registered with the Kubernetes apiserver:

Once this is done, there are two ways to run the operator:

1. Run as a Deployment inside the cluster

Build the memcached-operator image and push it to your registry. The following example uses https://quay.io as the registry.

Note If you are performing these steps on OSX, use the following sed command instead:

The above command will replace the string REPLACE_IMAGE with the : built above. Afterwards, verify that your operator.yaml file was updated successfully.

IMPORTANT: Ensure that your cluster is able to pull the image pushed to your registry.

Setup RBAC and deploy the memcached-operator:

Verify that the memcached-operator Deployment is up and running:

Verify that the memcached-operator pod is up and running:

IMPORTANT: Ensure that you built and pushed the image, and updated the operator.yaml file.

Verify that the operator is running successfully by checking its logs.

The following error will occur if your cluster was unable to pull the image:

Following the logs in the error scenario described above.

2. Run locally outside the cluster

This method is preferred during development cycle to deploy and test faster.

Create a Memcached CR

Create the example Memcached CR that was generated at deploy/crds/cache.example.com_v1alpha1_memcached_cr.yaml :

Ensure that the memcached-operator creates the deployment for the CR:

Check the pods and CR status to confirm the status is updated with the memcached pod names:

Update the size

Change the spec.size field in the memcached CR from 3 to 4 and apply the change:

Confirm that the operator changes the deployment size:

Delete the operator and its related resources:

The above walkthrough follows a similar implementation process to the one used to produce the memcached-operator in the SDK samples repo.

Manage the operator using the Operator Lifecycle Manager

NOTE: This section of the Getting Started Guide is out-of-date. We’re working on some improvements to Operator SDK to streamline the experience of using OLM. For further information see, for example, this enhancement proposal. In the meantime, you might find the following documentation helpful:

The previous section has covered manually running an operator. In the next sections, we will explore using the Operator Lifecycle Manager (OLM) which is what enables a more robust deployment model for operators being run in production environments.

OLM helps you to install, update, and generally manage the lifecycle of all of the operators (and their associated services) on a Kubernetes cluster. It runs as an Kubernetes extension and lets you use kubectl for all the lifecycle management functions without any additional tools.

NOTE: Various public, OLM-ready operator projects are available at operatorhub.io.

Generate an operator manifest

The first step to leveraging OLM is to create a Cluster Service Version (CSV) manifest. An operator manifest describes how to display, create and manage the application, in this case memcached, as a whole. It is required for OLM to function.

The Operator SDK CLI can generate CSV manifests via the following command:

Several fields must be updated after generating the CSV. See the CSV generation doc for a list of required fields, and the memcached-operator CSV for an example of a complete CSV.

NOTE: You are able to preview and validate your CSV manifest syntax in the operatorhub.io CSV Preview tool.

The next step is to ensure your project deploys correctly with OLM and runs as expected. Follow this testing guide to deploy and test your operator.

NOTE: Also, check out some of the new OLM integrations in operator-sdk:

Promoting operator standards

We recommend running operator-sdk scorecard against your operator to see whether your operator’s OLM integration follows best practices. For further information on running the scorecard and results, see the scorecard documentation.

NOTE: the scorecard is undergoing changes to give informative and helpful feedback. The original scorecard functionality will still be available while and after changes are made.

Hopefully, this guide was an effective demonstration of the value of the Operator Framework for building and managing operators. There is much more that we left out in the interest of brevity. The Operator Framework and its components are open source, so please feel encouraged to jump into each individually and learn what else you can do. If you want to discuss your experience, have questions, or want to get involved, join the Operator Framework mailing list.

About

An end-to-end scenario showing how to use the Operator Framework.

C++ : How to get element by index in vector | at() vs operator []

In this article we will discuss different techniques to get an element from vector by index or position.

In vector elements are indexed from 0 to size() – 1. To access any element in vector by index vector provides two member functions i.e.

Let’s discuss them in detail,

Access an element in vector using operator []

std::vector provides [] operator i.e.

It returns the reference of element in vector at index n.

Suppose we have a vector of int i.e.

Let’s access element at index 3 using operator [] i.e.

Access and update element in vector using []

As, operator [] returns a reference to the element in vector, so we can change the content of vector too using operator [] i.e.

It will update the value of element at index 3. New contents of vector will be,

We can also keep the returned reference in a reference variable and use later to modify the vector i.e.

New contents of vector will be,

Accessing out of index element through operator []

While accessing any element through operator [] we need to make sure that given index is in range i.e. less than the size of vector, otherwise it will result in undefined behaviour and can also crash application.

Therefore we should always check the size before accessing element using operator [] i.e.

Access an element in vector using vector::at()

std::vector provides an another member function at() i.e.

It returns the reference of element at index n in vector. If index n is out of range i.e. greater then size of vector then it will throw out_of_range exception.

Let’s access element at index 3 using at() i.e.

As at() returns a reference, so we can modify the value of element too i.e.

Accessing out of range element using at()

vector::at() will throw out_of_range exception in case we try to access the out of range element i.e.

Output:

vector::operator[] vs vector::at()

Both operator[] & at() provides random access to elements in vector in O(1) Complexity. But in case of out of range access operator[] causes undefined behaviour, whereas at() returns proper out_of_range exception. So, at() is more safe to use as compared to operator[].

Complete example is as follows,

Output:

To compile the above code use following command,

g++ –std=c++11 example.cpp

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We have curated a list of Best C++ Courses, that will teach you the cutting edge Modern C++ from the absolute beginning to advanced level. It will also introduce to you the word of Smart Pointers, Move semantics, Rvalue, Lambda function, auto, Variadic template, range based for loops, Multi-threading and many other latest features of C++ i.e. from C++11 to C++20.

Remember, C++ requires a lot of patience, persistence, and practice. So, start learning today.

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JavaScript Operators

Example

Assign values to variables and add them together:

The assignment operator ( = ) assigns a value to a variable.

Assignment

The addition operator ( + ) adds numbers:

Adding

The multiplication operator ( * ) multiplies numbers.

Multiplying

JavaScript Arithmetic Operators

Arithmetic operators are used to perform arithmetic on numbers:

Arithmetic operators are fully described in the JS Arithmetic chapter.

JavaScript Assignment Operators

Assignment operators assign values to JavaScript variables.

The addition assignment operator ( += ) adds a value to a variable.

Assignment

Assignment operators are fully described in the JS Assignment chapter.

JavaScript String Operators

The + operator can also be used to add (concatenate) strings.

Example

The result of text3 will be:

The += assignment operator can also be used to add (concatenate) strings:

Example

The result of text1 will be:

When used on strings, the + operator is called the concatenation operator.

Adding Strings and Numbers

Adding two numbers, will return the sum, but adding a number and a string will return a string:

Example

The result of x, y, and z will be:

If you add a number and a string, the result will be a string!

JavaScript Comparison Operators

JavaScript Logical Operators

Logical operators are fully described in the JS Comparisons chapter.

JavaScript Type Operators

Type operators are fully described in the JS Type Conversion chapter.

JavaScript Bitwise Operators

Bit operators work on 32 bits numbers.

Any numeric operand in the operation is converted into a 32 bit number. The result is converted back to a JavaScript number.

0101

The examples above uses 4 bits unsigned examples. But JavaScript uses 32-bit signed numbers.
Because of this, in JavaScript,

00000000000000000000000000000101 will return 11111111111111111111111111111010

Bitwise operators are fully described in the JS Bitwise chapter.

How to Overload Operators in C++

Classes are user-defined types. They allow us to represent the meaning of various entities. Defining an operator for a class gives us a better way to deal with objects.

So how can we define operators for our classes, and how should we use such operators? I will show you how in this article.

What are Operators in C++?

Operators are symbols which are used to perform operations on various operands. For example:

What is Operator Overloading in C++?

Let’s check out an example first.

For an integer type, the + operator gives the sum of two numbers, and for the string type it concatinates (joins) them.

So, operator overloading is all about giving new meaning to an operator. But:

So, basically what I mean is you cannot redefine an operator and you can’t create a new operator, either.

If you wished to create new operator like ** for exponential purposes, you couldn’t do it.

How does overloading work?

So operator overloading lets us define the meaning of an existing operator (note that you cannot overload some operators) for the operands of a user defined type (for example, a class is a user defined type).

Overloaded operators are just functions (but of a special type) with a special keyword operator followed by the symbol of the operator to be overloaded.

As I already mentioned, overloaded operators are just a special type of functions. They must have a return type, and parameters are always optional (as per their requirements).

So let’s overload some operators for our class now to see how it works:

Here we have two functions as a member function with the syntax mentioned above. So first let’s understand the syntax.

Both of the functions here return an object of Complex type. The operator keyword followed by the operators symbol tells us which operator is being overloaded.

We also have a display function to allow us to see the display of the object’s member values. We will substituted this with the overloaded operator ( ) later in the post.

How to Overload the Binary Plus (+) Operator in C++

Let’s overload the + operator now.

After this definition, if we do the following:

It should be clear that c1+c2 is equivalent to this:

After the call to the member function display, the output looks like this:

How to Overload the Binary Minus (-) Operator in C++

Now let’s overload the minus operator.

So this is how we overload operators in c++. Let’s now discuss the number of parameters that should be passed in the function.

The number of parameters passed to the function is equal to the number of operands taken by the operator.

But in case of a (non-static) member function, the number of parameters reduces by one. This is because the (non-static) member function somehow knows the object it was invoked for.

Isn’t that fun? Let’s now overload more operators for our class.

How to Overload the Not Equal To (!=) Operator in C++

The return type is a bool, so it returns either true or false.

How to Overload the Equal To (==) Operator in C++

Similarly for the operator == :

How to Overload the Get From ( operator. It will be fun!

Let’s see the function declaration first:

There are few changes from the previous functions. Let’s understand it more clearly.

The function is a friend function. This means that it is not within the scope of any class and cannot be invoked by an object. Also the function returns a reference to the ostream object and it takes two arguments as parameters:

You might be wondering why a friend function? Let’s talk about why we need friend functions now.

If an operator function is a (non-static) member function, then the left hand side operand will be bound to the this pointer that refers to the object which is calling the function.

We can define the operator like this for our class.

So in this way we can overload most of the operators for our class.

Some Operators Can’t Be Overloaded in C++

We cannot overload the following operators in c++:

They take a name, rather than a value, as their second operand and provide a primary means of referring to members. Allowing them to be overloaded would lead to subtleties. [Stroustroup, 1994]

Moreover the ternary operator (?:) and the named operators sizeof and typeid also cannot be overloaded.

Errors to Keep in Mind

Also remember that the following declaration is an error:

As mentioned earlier, Redefining an operator for built in type is an error.

One last point