Joseph-Mutua / microservicesBlog

A simple blog built on a micrservices architecture

Microservices

Microservices vs Monolith

A Monolith contains: Routing, Middlewares, Business Logic and Database Access to implement all features of an app while a Microservice contains: Routing, Middlewares, Business Logic and Database Access to implement only one feature of an app.

Reasons for Database-Per-Service

1. To enable each service to run independently of other services
2. The Database schema/structure might change unexpectedly
3. Some services might function more efficiently with different types of Databases (SQL vs noSQL)

Communicataion Strategies Between Services

1. Sync Services communicate with each other using direct requests.
2. Async Services communicate with each other using events.

Event Buses

• Different implementations: RabbitMQ, Kafka, NATS
• Receives events, publishes them to listeners

Deployment Issues

Docker

Docker containers wrap up everything that is needed for a program + how to start and run it

Kubernetes

A tool for running a bunch of different containers. It is given some configuration to describe how we want our containers to run and interact with each other.

Kubernetes Cluster: Contains a bunch of nodes controlled by a master

Docker

Makes it really easy to install and run software without worrying about setup or dependencies

Docker Ecosystem

• Docker Client(CLI): Tool that we are going to issue commands to.
• Docker Server(Daemon): Tool that is responsible for creating images, running containers, etc
• Docker Machine
• Docker Hub
• Docker Images: A docker image is a template that contains the application, and all the dependencies required to run that application on Docker i.e code, runtime, system tools, system libraries and settings.
• Docker Compose

Docker Container: A running instance of the Docker image. i.e a standard unit of software that packages up code and all its dependencies so the application runs quickly and reliably from one computing environment to another.

Namespacing Isolating resources per process(or group of processes) Control Groups(cGroups) Limit amount of resources used per process.

Starting with a Shell Execute an additional command in a container: docker exec -it <container id> <command>: e.g docker run -it busybox sh

• docker Reference the docker client
• exec Run another command
• -it Allow us to provide input to the container
• container id ID of the container
• Command to execute

Creating a Dockerfile

1. Specify a base image
2. Run some commands to install additional programs
3. Specify a command to run on container startup

Tagging an image

docker build -t josephmutua/redis:latest .

• -t josephmutua/redis Tags the image
• . Specifies the directory of files/folders to use for the build

Project

1. Create NodeJS web app
2. Create a dockerfile
3. Build image from dockerfile
4. Run image as container
5. Connect to web app from browser

Basic Docker Commands

1. docker build -t joseph/posts Build an image based on the dockerfile in the current directory. Tag it as "joseph/posts"
2. docker run [image id or image tag] Create and start a container based on the provided image id or tag.
3. docker run -it[image id or image tag][cmd] Create and start container, but also override the default command.
4. docker ps Print out info about all of the running containers
5. docker exec -it[container id][cmd] Execute the given command in a running container.
6. docker logs[container id] Print out logs from the given container.

Load Balancers and Ingress

Load Balancer Service Tells Kubernetes to reach out to its provider and provision a load balancer. Gets traffic into a single pod.

Ingress/Ingress Controller A pod with a set of routing rules to distribute traffic to other services.