Mongo Replica Set using Terraform

Allows creating several instances with MongoDB 3.2 enabling Replica set mode into all instances created. MongoDB Replica set infrastructure into VPC. It includes:

• Instance
• Security Group
• Elastic IP

Consider Fault Tolerance

Number of Members	Majority Required to Elect a New Primary	Fault Tolerance
3	2	1
4	3	1
5	3	2
6	4	2

For this case, it was configurated 3 instances.

Set Replica Set into Instances

1. terraform apply: Apply the changes required to builds instances with Mongo 3.2.

2. The replica Set configuration is a manual configuration yet. The steps to define it are:

   2.1. rs.initiate(): Initiate instance in Replica Set mode. Use it on one only one member of the replica set. 2.2. mongo: Loggin into mongo to add other hosts. 2.3. rs.add( {host:"<host/ip:port>", priority: 0, votes: 0} ): Add each one of instance to replica set. When a newly added secondary has its votes and priority settings greater than zero, during its initial sync, the secondary still counts as a voting member even though it cannot serve reads nor become primary because its data is not yet consistent. 2.4. Once the newly added member has transitioned into SECONDARY state, use rs.reconfig() to update the newly added members priority and votes if needed.

   var cfg = rs.conf();
   cfg.members.forEach( function(member) {
       member.votes = 1;
       member.priority = 1;
   });
   rs.reconfig(cfg);
   

   2.5. rs.config(): Show new configuration.

Commands

terraform init -> Initialize terraform

terraform plan -> Show plan description from files

terraform apply -> Apply plan

terraform destroy -> Destroy plan

Considerations

• This project uses terraform to build all elements into Amazon.
• Create <home path>/.aws/credentials with access and secrets key to AWS.
• This project needs a VPC with subnet to can build infrastructure.

References

https://www.terraform.io/

https://docs.mongodb.com/v3.2/tutorial/expand-replica-set/