AWS Cloudformation - Installing packages with cfn-init - bash

Question

I have created an EC2 instance via cloudformation and I am trying to get it to install postgres on the instance directly via cloudformation. However, when I SSH into my instance and try to run psql via the command line I keep getting:
bash: psql: command not found
I have tried doing it manually, installing postgres with the below command and it works fine.
sudo yum install postgresql postgresql-server postgresql-devel postgresql-contrib postgresql-docs
Could it be that it is because I'm just updating the stack and thus the ec2 instance rather than creating a new one?
Below is a snippet from the cloudformation template. Everything works when I update the template but it seems that postgres still isn't installed...
DbWrapper:
Type: AWS::EC2::Instance
Metadata:
AWS::CloudFormation::Init:
config:
packages:
yum:
postgresql: []
postgresql-server: []
postgresql-devel: []
postgresql-contrib: []
postgresql-docs: []
Properties:
ImageId: ami-f976839e #AMI aws linux 2
InstanceType: t2.micro
AvailabilityZone: eu-west-2a
SecurityGroupIds:
- !Ref Ec2SecurityGroup
SubnetId: !Ref SubnetA
KeyName: !Ref KeyPairName
UserData:
Fn::Base64:
!Join [ "", [
"#!/bin/bash -xe\n",
"sudo yum update\n",
"sudo yum install -y aws-cfn-bootstrap\n", #download aws helper scripts
"sudo /opt/aws/bin/cfn-init -v ", #use cfn-init to install packages in cloudformation init
!Sub "--stack ${AWS::StackName} ",
"--resource DbWrapper ",
"--configsets Install ",
!Sub "--region ${AWS::Region} ",
"\n" ] ]

Answer 1

If anyone is encountering the same problem, the solution was indeed that you need to delete the instance and recreate from scratch. Just updating the stack won't work.

Answer 2

A bit late here (I found this searching for another issue), but you can re-run your CF Launch Config with this piece from your snippet:
UserData:
Fn::Base64:
!Join [ "", [
"#!/bin/bash -xe\n",
"sudo yum update\n",
"sudo yum install -y aws-cfn-bootstrap\n", #download aws helper scripts
"sudo /opt/aws/bin/cfn-init -v ", #use cfn-init to install packages in cloudformation init
!Sub "--stack ${AWS::StackName} ",
"--resource DbWrapper ",
"--configsets Install ",
!Sub "--region ${AWS::Region} ",
"\n" ] ]
the /opt/aws/bin/cfn-init command is what's running the metadata config from the launch config you've specified, which is where your packages are defined.
https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/cfn-init.html
The reason deleting the instance and recreating it works is that it re-runs the UserData piece from the EC2 section above.

Answer 3

This is related to you calling cfn-init with --configsets value that you do not have defined. You would need to add the configSets section below to your metadata section:
Metadata:
AWS::CloudFormation::Init:
configSets:
Install:
- "config"
config:
packages:
yum:
postgresql: []
postgresql-server: []
postgresql-devel: []
postgresql-contrib: []
postgresql-docs: []
Otherwise take out --configset from your cfn-init original call.
References:
cfn-init
AWS::CloudFormation::Init