Let's get some hands-on on the docker swarm. Docker swarm is one of the most important things which we would need to use on our production. So let's get started to absorb some new skills.

Idea is to make 2 docker files

• For Mongo
• A python script that will respond to a mongo triggers as soon as possible.

For-example : Suppose I am a client and I just created a request to buy something,I hire docker swarms as a manager which will hire and fire customer sales representatives on the bases of failed tasks. Now as a Bussiness owner (In real i'm a storyteller who is building this story to make this thing excited) I want my docker swarm to manage things so that my every clinet would get response in a minimal time to increase my customer satisfaction. According to resources I have I asked my manager (docker swarm) to hire only 3 CSR at time, **and now comes the boss stage for testing purpose I will do 1000 requests at a single time to see how the manager and CSR will handle those 1000 customer (evil smile).

First we will setup our mongo servers and mongo replicas. We need mongo replicas because it is a requirment of mongo to build replica of database first to listen for triggers. So Lets build Mongo Servers.

1. Pull Mongo Image

docker pull mongo:4

2. Create Docker Network

docker network create mongo-cluster-dev

3. Run mongo Containers

docker run -d --net mongo-cluster-dev -p 27017:27017 --name mongoset1 mongo:4 mongod --replSet mongodb-replicaset --port 27017
docker run -d --net mongo-cluster-dev -p 27018:27018 --name mongoset2 mongo:4 mongod --replSet mongodb-replicaset --port 27018
docker run -d --net mongo-cluster-dev -p 27019:27019 --name mongoset3 mongo:4 mongod --replSet mongodb-replicaset --port 27019

4. Add This to your /etc/hosts file

sudo nano /etc/hosts
Append in the end of file:

127.0.0.1       mongoset1 mongoset2 mongoset3

5. Add replica information to your primary Node

docker exec -it mongoset1 mongo

# Run this after getting into the mongo container

db = (new Mongo('localhost:27017')).getDB('test')
config={"_id":"mongodb-replicaset","members":[{"_id":0,"host":"mongoset1:27017"},{"_id":1,"host":"mongoset2:27018"},{"_id":2,"host":"mongoset3:27019"}]}
rs.initiate(config)

You will get results like this

{
	"ok" : 1,
	"$clusterTime" : {
		"clusterTime" : Timestamp(1567674525, 1),
		"signature" : {
			"hash" : BinData(0,"AAAAAAAAAAAAAAAAAAAAAAAAAAA="),
			"keyId" : NumberLong(0)
		}
	},
	"operationTime" : Timestamp(1567674525, 1)
}

6. Ok Now You can use this string as a connection string

mongodb://<hostname>:27017,<hostname>:27018,<hostname>:27019/<Your database name>?replicaSet=mongodb-replicaset

7. Test your setup with the help of this notebook Testing

Okay! Lets get started with the python scripts. We will make 2 scripts

1. 1st is our CSR (customer sales representative) worker script
2. 2nd will be the testing script

In this script we will write code to listen mongo insert triggers and perform some opertaion on the inserted mongo-document

This script will helps us to insert, find and delete requests from the mongo database.

Kindly Speceify Mongo Url in env file. Python Script will automatically get the url and run insert triggers on the following database

Pull Docker Image

docker pull sohaibanwaar/mongo-triggers-testing

Start docker swarm

sudo docker service create --replicas 5 --name mongo -e MONGO_URL="Your Mongo URL" sohaibanwaar/mongo-triggers-testing

Htop on the upper side represents mongo server and on the below on docker swarm replicas of python script are running.

1. Docker Replica Set
2. Missing Requests Question
3. Mongo Communication Question
4. Docker Link