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This is a very good question and I went through this very painful journey myself recently. I am writing a fairly extensive answer here in the hope that some of these thoughts of running a MongoDB cluster via CloudFormation are useful to others.I’m assuming that you’re creating a MongoDB production cluster as follows: -3 config servers (micros/smalls instances can work here)At least 1 shard consisting of e.g. 2 (primary & secondary) shard instances (minimum or large) with large disks configured for data / log / journal disks.arbiter machine for voting (micro probably OK).i.e. https://docs.mongodb.org/manual/core/sharded-cluster-architectures-production/Like yourself, I initially tried the AWS MongoDB CloudFormation template that you posted in the link (https://s3.amazonaws.com/quickstart-reference/mongodb/latest/templates/MongoDB-VPC.template) but to be honest it was far, far too complex i.e. it’s 9,300 lines long and sets up multiple servers (i.e. replica shards, configs, arbitors, etc). Running the CloudFormation template took ages and it kept failing (e.g. after 15 mintues) which meant the servers all terminated again and I had to try again which was really frustrating / time consuming.The solution I went for in the end (which I’m super happy with) was to create separate templates for each type of MongoDB server in the cluster e.g.MongoDbConfigServer.template (template to create config servers – run this 3 times)MongoDbShardedReplicaServer.template (template to create replica – run 2 times for each shard)MongoDbArbiterServer.template (template to create replica – run once for each shard)NOTE: templates available at https://github.com/adoreboard/aws-cloudformation-templatesThe idea then is to bring up each server in the cluster individually i.e. 3 config servers, 2 sharded replica servers (for 1 shard) and an arbitor. You can then add custom parameters into each of the templates e.g. the parameters for the replica server could include: -InstanceType e.g. t2.microReplicaSetName e.g. s1r (shard 1 replica)ReplicaSetNumber e.g. 2 (used with ReplicaSetName to create name e.g. name becomes s1r2)VpcId e.g. vpc-e4ad2b25 (not a real VPC obviously!)SubnetId e.g. subnet-2d39a157 (not a real subnet obviously!)GroupId (name of existing MongoDB group Id)Route53 (boolean to add a record to an internal DNS – best practices)Route53HostedZone (if boolean is true then ID of internal DNS using Route53)The really cool thing about CloudFormation is that these custom parameters can have (a) a useful description for people running it, (b) special types (e.g. when running creates a prefiltered combobox so mistakes are harder to make) and (c) default values. Here’s an example: – “Route53HostedZone”: { “Description”: “Route 53 hosted zone for updating internal DNS (Only applicable if the parameter [ UpdateRoute53 ] = \”true\””, “Type”: “AWS::Route53::HostedZone::Id”, “Default”: “YA3VWJWIX3FDC” },This makes running the CloudFormation template an absolute breeze as a lot of the time we can rely on the default values and only tweak a couple of things depending on the server instance we’re creating (or replacing).As well as parameters, each of the 3 templates mentioned earlier have a “Resources” section which creates the instance. We can do cool things via the “AWS::CloudFormation::Init” section also. e.g.”Resources”: { “MongoDbConfigServer”: { “Type”: “AWS::EC2::Instance”, “Metadata”: { “AWS::CloudFormation::Init”: { “configSets” : { “Install” : [ “Metric-Uploading-Config”, “Install-MongoDB”, “Update-Route53” ] },The “configSets” in the previous example shows that creating a MongoDB server isn’t simply a matter of creating an AWS instance and installing MongoDB on it but also we can (a) install CloudWatch disk / memory metrics (b) Update Route53 DNS etc. The idea is you want to automate things like DNS / Monitoring etc as much as possible.IMO, creating a template, and therefore a stack for each server has the very nice advantage of being able to replace a server extremely quickly via the CloudFormation web console. Also, because we have a server-per-template it’s easy to build the MongoDB cluster up bit by bit.My final bit of advice on creating the templates would be to copy what works for you from other GitHub MongoDB CloudFormation templates e.g. I used the following to create the replica servers to use RAID10 (instead of the massively more expensive AWS provisioned IOPS disks).https://github.com/CaptainCodeman/mongo-aws-vpc/blob/master/src/templates/mongo-master.templateIn your question you mentioned auto-scaling – my preference would be to add a shard / replace a broken instance manually (auto-scaling makes sense with web containers e.g. Tomcat / Apache but a MongoDB cluster should really grow slowly over time). However, monitoring is very important, especially the disk sizes on the shard servers to alert you when disks are filli
Source: amazon web services – Mongodb cluster with aws cloud formation and auto scaling – Stack Overflow