El nucleo de la programacion asincrona son los objetos Task y Task<T>. Ambos son compatibles con las palabras clave async y await.

Primero hay que identificar si el codigo se usa para trabajos enlazados a I/O o si estos son CPU intensivos.

• Si el codigo espera algo como una BBDD o una response de un servidor, es codigo I/O. En este caso hay que usar async y await
• Si el codigo realiza un calculo costoso, es CPU intensivo. Use await para esperar una operacion que se ha comenzado en background con Task.run

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Middleware is software assembled into a pipeline to handle request and responses. Each component:

• Chooses if he passes the request to the next component.
• Can perform work before and after the next component.

Common use cases:

• Logging
• Authentication & Authorization
• Request/Response processing
• Caching
• Error handling

Implementation w. DI

We create our own custom middleware with an internal dependency, which is the class it’s going to process before/after our request.

// interface and its class, which do the processing
public interface IMiddlewareService
{
	Task ProcessRequest(string request);
}

// interface implementation
public class MiddlewareService : IMiddlewareService
{
	public async Task ProcessRequest(string request)
	{
		// do something with the request
		Console.WriteLine(request);
	}
}

Then we have our middleware class as such

public class CustomMiddleware(IMiddlewareService _service) : IMiddleware
{
	public async Task InvokeAsync(HttpContext context, RequestDelegate next)
	{
		// custom logic to be executed BEFORE next middleware
		await _service.ProcessRequest("middleware processing request");
		await next(context);
		// custom logic to be executed AFTER next middleware
	}
}

Declaration inside Startup.cs

public void ConfigureServices(IServiceCollection services)
{
	// ... whatever

	// register both: our custom middleware, and its internal dependency
	services.AddTransient<IMiddlewareService, MiddlewareService>();
	services.AddTransient<CustomMiddleware>();
	
	// ... whatever else
}

public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
{
	// ... whatever

	// declaration to use middleware
	app.UseMiddleware<CustomMiddleware>();
	// if we use this, the middleware declaration has to be BEFORE or else it won't work
	app.UseEndpoints(endpoints => 
	{
		endpoints.MapControllers();
	})

	// ... whatever else
}

Reference(s)

https://medium.com/@dushyanthak/best-practices-for-writing-custom-middlewares-in-asp-net-core-97b58c50cf9c
https://learn.microsoft.com/es-es/aspnet/core/fundamentals/middleware/write?view=aspnetcore-8.0
https://sardarmudassaralikhan.medium.com/custom-middleware-in-asp-net-core-web-api-70c2ffbbc095

We can set pre-request scripts (run before the request) & tests (after execution) at several levels:

• Collection
• Folder
• Request

Snippets

Inside pre-request Script and Tests we have a SNIPPETS column with templates we may use for our code.

Get / Set variables

console.log("Hello world");

// work with local vars
let urlVar = pm.variables.get("protocol");
console.log("value for protocol: " + urlVar);

pm.variables.set("protocol", "http");
console.log(pm.variables.get("protocol"));  

// work with global vars
let globalVar = pm.globals.get("env");
console.log(globalVar);

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To test postman I use https://reqres.in. You can use it to learn how to write Postman tests.

Collections

Collections have metadata which you can set up. This includes:

• Authorization so you don’t need to set it for every single request.
• Variables, for variables only for this collection (so you don’t use environment vars).
• Collection tests.

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Hay un problema al intentar correr una imagen tuya propia en local con minikube. Minikube tiene su propio repositorio de imagenes y si no encuentra una imagen alli, la intenta descargar siempre del repositorio.

Solución

Set imagePullPolicy: IfNotPresent

Run the following command:

eval $(minikube docker-env)
# build again the image
# try to run it again

Reference(s)

https://medium.com/bb-tutorials-and-thoughts/how-to-use-own-local-doker-images-with-minikube-2c1ed0b0968

Config

Azure

log-in into a tenant

az login --tenant 7f2c3a6b-e849-4d6f-b65d-1c0ef8b0f41c

configure local kubectl .kube config file

az aks get-credentials --resource-group my-aks --name aksname --admin

(the –admin part is optional but useful)

Contexts & Namespaces

see all configured contexts

kubectl config get-contexts

configure a context with a default namespace

kubectl config set-context <context_here> --namespace=<namespace_here>
# example
kubectl config set-context my-aks-context --namespace=aks-dev

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Data generated and used by Docker containers does not persist after restarts. We use Docker volumes to manage data to solve this issue. We use it to persist data in a container or share data between containers.

Volumes are the preferred mechanism for persisting data generated and user by Docker containers. Volumes are easier to back up or migrate.

Volumes are often a better choice than persisting data in a container’s writable layer, because a volume does not increase the size of the containers using it. The volume’s contents exist outside the lifecycle of a given container.

We have 3 volume types:

Anonymous volumes

Helpful to persist data temporarily. If we restart our container data is still visible. It doesn’t persist when we remove the container. Not accessible by other containers. They’re created inside /var/lib/docker/volume.

Example file:

version: '3.8'  
services:  
  db:  
    image: mysql  
    restart: always  
    environment:  
      MYSQL_ROOT_PASSWORD: root  
      MYSQL_DATABASE: test_db  
    ports:  
      - "3306:3306"  
    volumes:  
      - /var/lib/mysql

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Steps to go from a docker-compose file, to build an Image out of the file, upload it to DockerHub, and run it with Kubernetes (minikube).

Set up

Install Kompose

# linux
curl -L https://github.com/kubernetes/kompose/releases/download/v1.22.0/kompose-linux-amd64 -o kompose
chmod +x kompose
sudo mv ./kompose /usr/local/bin/kompose

Clone App and Host It into DockerHub

Clone the files, go to the directory where your Dockerfile is and run:

# mariocodes is my DockerHub username
# kubernetes-custom-java-maven-app is the name of the repo I created at DockerHub
docker build -f Dockerfile -t mariocodes/kubernetes-custom-java-maven-app .

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(Oficial Doc)

Technology to quickly set up a Kubernetes cluster locally to learn how to use Kubernetes.

Installation

How to install on a fresh Ubuntu installation:

Install prerrequisites and kubectl

sudo apt-get update && sudo apt-get install -y apt-transport-https curl

curl -s https://packages.cloud.google.com/apt/doc/apt-key.gpg | sudo apt-key add -

echo "deb https://apt.kubernetes.io/ kubernetes-xenial main" | sudo tee -a /etc/apt/sources.list.d/kubernetes.list

sudo apt-get update
sudo apt-get install -y kubectl

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STATUS CrashLoopBackOff

CrashLoopBackOff and no log appears. This happens as the container has no command to run so it start up and then immediately exits.

Give your image a command.

more here

apiVersion: v1
kind: Pod
metadata:
  name: twocontainers
spec:
  containers:
  - name: container1
    image: python:3.6-alpine
	command: ['sh', '-c', 'echo cont1 > index.html && python -m http.server 8082']
  - name: container2
    image: python:3.6-alpine
	command: ['sh', '-c', 'echo cont1 > index.html && python -m http.server 8083']

Relational

SQL

SQL Cheat Sheet
SQL Triggers & Stored Procedures
SQL Views & Materialized views

PgSQL Functions

PgSQL Functions (Stored Procedure)

MySQL

MySQL Administration
MySQL User Privileges

No-relational

Mongo

MongoDB

ElasticSearch

ElasticSearch