Using SSH Agent in Jenkins to connect to multiple instances - amazon-web-services

Question

I created a pipeline job that connects to an AWS account and runs some shell scripts.
At one point I wanted to add an SSH step, in which Jenkins ssh into each instance inside the account, performs an update and a restart, then continues until all instances are updated.
Account is comprised of 4 instances, grouped into pairs.
This is my Jenkinsfile (the ssh part is commented out for now):
pipeline {
agent {
label "amazon-small"
}
stages {
stage('Repo Checkout') {
steps {
git credentialsId: 'jenkins-ssh', url: 'ssh://git#REPO.git'
}
}
stage('Create snapshots') {
withAWS(role: "${config.aws_role}", roleAccount: "${config.aws_acount}", duration: 3600) {
steps {
sh "aws_patch_stuff/snapshots.sh"
}
}
}
stage('Deregister first ID pair from target group') {
steps {
sh "source vars.sh; deregister_pair_from_target_group ${id_pair_1[#]}"
}
}
stage('SSH into first host pair, update and restart') {
steps {
sshagent(credentials: [config.credential_id]) {
sh "python3 check_active_sessions.py"
// sh "source vars.sh; ssh_into_pair ${ip_pair_1[#]}"
}
}
}
stage('Register targets after reboot') {
steps {
sh "source vars.sh; register_pair_to_target_group ${id_pair_1[#]}"
}
stage('Check software availability') {
steps {
sh "source vars.sh; check_soft_availability ${ip_pair_1[#]}"
}
}
stage('Deregister second ID pair from target group') {
steps {
sh "source vars.sh; deregister_pair_from_target_group ${id_pair_2[#]}"
}
}
stage('SSH into second host pair, update and restart') {
steps {
sshagent(credentials: [config.credential_id]) {
sh "python3 check_active_sessions.py"
// sh "source vars.sh; ssh_into_pair ${ip_pair_2[#]}"
}
}
}
stage('Register targets after reboot') {
steps {
sh "source vars.sh; register_pair_to_target_group ${id_pair_2[#]}"
}
}
stage('Check software availability') {
steps {
sh "source vars.sh; check_soft_availability ${ip_pair_2[#]}"
}
}
post {
always {
script {
currentBuild.result = currentBuild.result ?: 'SUCCESS'
mail bcc: '', body: 'Update done, hosts rebooted, packages are up to date', cc: '', from: '', replyTo: '', subject: 'Status for update and reboot pipeline', to: 'some.name#email.com'
}
}
}
}
The ssh function looks like this:
ssh_into_pair () {
arr=("$#")
for INSTANCEIP in ${arr[#]}
do
echo "Updating $INSTANCEIP..."
ssh -o StrictHostKeyChecking=no -l ec2-user $INSTANCEIP uname -a
sudo yum update
echo "Performing restart..."
sudo needs-restarting -r || sudo shutdown -r 1
sleep 10
done
}
I tried using the SSH plugin for Jenkins, however I am pretty sure I'm not using it right.
The private keys are stored in jenkins and are provided in the groovy file of the job, so this should't be an issue. Is there a way I can actually achieve this? Should I maybe consider using Ansible as well?