AWS has its own continuous integration tool known as CodeDeploy, using a simple command you would be able to deploy on multiple servers when you want to change something on code base.

Installing code deploy to instance

If code deploy client is not installed at your instance, you would need to do that:

sudo yum install -y ruby wget
cd /opt
wget https://aws-codedeploy-ap-south-1.s3.amazonaws.com/latest/install
chmod +x ./install
sudo ./install auto

Create CodeDeploy Application

You have to create Code Deploy application with Deployment type to Inplace deployment, and deployment Configuration set to CodeDeployDefault.OneAtATime.
Give it a name under Ec2 configuration and Amazon ec2 instance, say the name is Code deploy instance. Now you have to add the same tag to all your code deploy instances.

Set IAM Permissions

Now that we are done with installation, we would need to setup IAM rules:
First create an IAM group called CodeDeployGroup. This group needs AmazonS3FullAccess and AWSCodeDeployFullAccess permissions. Create a user and add it to this group. This user only needs programmatic access.Save key and key id to somewhere safe.

Create role that has Trusted entities and Policies are ec2.amazonaws.com and AWSCodeDeployRole AmazonS3FullAccess, respectively.

Edit trust relationship to following:

{
  "Version": "2012-10-17",
  "Statement": [
    {
      "Effect": "Allow",
      "Principal": {
        "Service": [
            "ec2.amazonaws.com",
            "codedeploy.ap-south-1.amazonaws.com"
        ]
      },
      "Action": "sts:AssumeRole"
    }
  ]
}

Create new s3 bucket with previously created IAM rules.

CodeDeploy configuration

My codebase  structure is something like following:

- src
  - <django project>
- scripts
   install_dependencies
   start_server
   stop_server
appspec.yml
codedeploy_deploy.py
deploy.sh

appspec.yml is the file that contains our hooks and configuration for code deploy.

version: 0.0
os: linux
files:
  - source: src
    destination: /home/centos/proj_name
hooks:
  BeforeInstall:
    - location: scripts/install_dependencies
      timeout: 300
      runas: root
  ApplicationStop:
    - location: scripts/stop_server
      timeout: 300
      runas: root
  ApplicationStart:
    - location: scripts/start_server
      timeout: 300
      runas: root

for django scripts/install_dependencies may look like following:

sudo yum install -y gcc openssl-devel bzip2-devel wget
sudo yum install -y make git
cd /opt
command -v python3.6 || {
    wget https://www.python.org/ftp/python/3.6.3/Python-3.6.3.tgz
    tar xzf Python-3.6.3.tgz
    cd Python-3.6.3
    sudo ./configure --enable-optimizations
    sudo make altinstall
}
sudo yum install -y mysql-devel

for scripts/start_server I have following:

cd /home/centos/evaly
pip3.6 install -r requirements.txt
nohup uwsgi --http :80 --module evaly.wsgi > /dev/null 2>&1 &

for scripts/stop_server I have following:

pkill uwsgi

I have borrowed a python script from bitbucket team which looks like following:

# Copyright 2016 Amazon.com, Inc. or its affiliates. All Rights Reserved.
#
# Licensed under the Apache License, Version 2.0 (the "License"). You may not use this file
# except in compliance with the License. A copy of the License is located at
#
#     http://aws.amazon.com/apache2.0/
#
# or in the "license" file accompanying this file. This file is distributed on an "AS IS"
# BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
# License for the specific language governing permissions and limitations under the License.
"""
A BitBucket Builds template for deploying an application revision to AWS CodeDeploy
narshiva@amazon.com
v1.0.0
"""
from __future__ import print_function
import os
import sys
from time import strftime, sleep
import boto3
from botocore.exceptions import ClientError

VERSION_LABEL = strftime("%Y%m%d%H%M%S")
BUCKET_KEY = os.getenv('APPLICATION_NAME') + '/' + VERSION_LABEL + \
    '-bitbucket_builds.zip'

def upload_to_s3(artifact):
    """
    Uploads an artifact to Amazon S3
    """
    try:
        client = boto3.client('s3')
    except ClientError as err:
        print("Failed to create boto3 client.\n" + str(err))
        return False
    try:
        client.put_object(
            Body=open(artifact, 'rb'),
            Bucket=os.getenv('S3_BUCKET'),
            Key=BUCKET_KEY
        )
    except ClientError as err:
        print("Failed to upload artifact to S3.\n" + str(err))
        return False
    except IOError as err:
        print("Failed to access artifact.zip in this directory.\n" + str(err))
        return False
    return True

def deploy_new_revision():
    """
    Deploy a new application revision to AWS CodeDeploy Deployment Group
    """
    try:
        client = boto3.client('codedeploy')
    except ClientError as err:
        print("Failed to create boto3 client.\n" + str(err))
        return False

    try:
        response = client.create_deployment(
            applicationName=str(os.getenv('APPLICATION_NAME')),
            deploymentGroupName=str(os.getenv('DEPLOYMENT_GROUP_NAME')),
            revision={
                'revisionType': 'S3',
                's3Location': {
                    'bucket': os.getenv('S3_BUCKET'),
                    'key': BUCKET_KEY,
                    'bundleType': 'zip'
                }
            },
            deploymentConfigName=str(os.getenv('DEPLOYMENT_CONFIG')),
            description='New deployment from BitBucket',
            ignoreApplicationStopFailures=True
        )
    except ClientError as err:
        print("Failed to deploy application revision.\n" + str(err))
        return False     
           
    """
    Wait for deployment to complete
    """
    while 1:
        try:
            deploymentResponse = client.get_deployment(
                deploymentId=str(response['deploymentId'])
            )
            deploymentStatus=deploymentResponse['deploymentInfo']['status']
            if deploymentStatus == 'Succeeded':
                print ("Deployment Succeeded")
                return True
            elif (deploymentStatus == 'Failed') or (deploymentStatus == 'Stopped') :
                print ("Deployment Failed")
                return False
            elif (deploymentStatus == 'InProgress') or (deploymentStatus == 'Queued') or (deploymentStatus == 'Created'):
                continue
        except ClientError as err:
            print("Failed to deploy application revision.\n" + str(err))
            return False      
    return True

def main():
    if not upload_to_s3('/Users/sadafnoor/Projects/evaly/artifact.zip'):
        sys.exit(1)
    if not deploy_new_revision():
        sys.exit(1)

if __name__ == "__main__":
    main()

I have written a script to zip up my source code so that the script can upload it to s3 and eventually all my ec2 instances will be downloading that zip from s3.

export APPLICATION_NAME="CodeDeployApplicationName" 
export AWS_ACCESS_KEY_ID="IAMUserKeyId"
export AWS_DEFAULT_REGION="ap-south-1"

export AWS_SECRET_ACCESS_KEY="IAMUserSecretKey"
export DEPLOYMENT_CONFIG="CodeDeployDefault.OneAtATime"

export DEPLOYMENT_GROUP_NAME="CodeDeployDeploymentGroup"
export S3_BUCKET="S3BucketName"
zip -r ../artifact.zip src/* appspec.yml scripts/*
python codedeploy_deploy.py