NATS - Microservice auto registering, discovery and messaging

We need a way to register each microservice instead of a static registration. Also, we need to check the health of each microservice without using HTTP because it could get into a conflict with some microservice routes. Also, we need to create a way to add microservices to the ecosystem dynamically, sure, with a security basis.

In order to it, we need to add to the microservice ecosystem NATS. Also, we need to specify a protocol, interface o some way to:

1. Microservice register on startup.
2. The gateway must check the availability of a microservice using NATS, for this, the gateway must have a table (in memory) with the currently registered microservices. If a request target to a microservice that is not registered in the table, then the Gateway must check the availability sending a message with NATS. If the microservice respond, the gateway adds the microservice to the table.

# Security
First of all, the gateway is the only microservices that is enabled to manage the microservice routing. In order to keep a secure flow, we need to update the docker-compose yaml file to provides a unique JWT token, or a common secret. The Gateway must have a Secret always (it is a mandatory), this secret will be used to generate new tokens to new Microservices.

## Requirements to register to the ecosystem

1. Each microservice must have or a JWT token or a secret, otherwise the microservice will not be registered.
2. The gateway Must Have a secret. If it does not exist, the gateway CANT START.

# Way to register a microservice

1. At startup: Each microservice send a message with the 'secret' or the JWT token, and its name to the gateway. If MS sends a Secret, the gateway validates the secret and send a token. If the MS sends a token, the gateway must validate it, and if the token or the secret is valid, then Gateway must add it to the Microservices table

2. a request to unknow microservices arrives: It could be happend if that microservice was not registered in the microservices table. Then, the Gateway must send a message to identify (PING), if it was not resolved (because the microservice doest not exist, or it is not properly configured), send a 404. Otherwise, if the microservice exists and it is properly configured, the microservice will send the token or the secret, and it will be registered as above.

# Messages namming

#### "gateway:ping"

- Listen by: children microservices
- Sended by: gateway

is a gateway message to discovery new microservices.

#### "gateway:login"

- Listen By: gateway
- Sended by: microservices that want to register to the ecosystem
- Data: {name:'myMs', token?:'tokenOrSecret',secret:?'tokenOrSecret' } , token or secret must be sent.

add myMs to the microservice table

#### "gateway:logout"

- Listen By: gateway
- Sended by: microservices that want to be removed from the ecosystem
- Data: {name:'myMs', token?:'tokenOrSecret',secret:?'tokenOrSecret' }, token or secret must be sent.

remove myMs from the microservice table