Docker

To run microservices on docker environment we need to create docker images for microservices.This document provides steps to create docker images for microservices.

Docker:

Docker is an open platform for developing, shipping, and running applications. Docker enables you to separate your applications from your infrastructure so you can deliver software quickly. With Docker, you can manage your infrastructure in the same ways you manage your applications.

Docker provides the ability to package and run an application in a loosely isolated environment called a container. The isolation and security allow you to run many containers simultaneously on a given host. Containers are lightweight because they don’t need the extra load of a hypervisor, but run directly within the host machine’s kernel. This means you can run more containers on a given hardware combination than if you were using virtual machines. You can even run Docker containers within host machines that are actually virtual machines

Docker Engine is a client-server application with these major components:

1. A server which is a type of long-running program called a daemon process (the dockerd command).
2. A REST API which specifies interfaces that programs can use to talk to the daemon and instruct it what to do.
3. A command line interface (CLI) client (the docker command).

Docker Swarm:

For running the MS as a container .we will use docker swarm architecture,

A swarm will consist of managers, nodes and services.
A node is basically a worker of your swarm, it will only receive instructions. 
A manager is a node that can give instructions to your swarm (i.e. creating and removing services). Managers can also run instances of services.

A service can have multiple replicas and Docker will distribute them evenly across your nodes – if you have 3 (active) nodes and a service with 3 replicas, each node will have a running instance of that service.

For any service in the swarm, Docker will do a round-robin between the replicas (shameless plug, watch Load balancing is impossible). Docker call this feature of distributing incoming connections from outside the swarm ingress load balancing. Is important to say that if you access a service from within the swarm it will also go through the built-in load balancer.

If you try to access a service on a node that’s not running it Docker will re-reoute the request to a node that has a running instance of that service.

Here the component labeled LB is serving as a reverse proxy and it will have to be able to discover new nodes in your swarm dynamically.