Helper to start an SSM session in an ec2 instance knowing its name

start_ssm_session.sh

# Starts an SSM session in an EC2 instance
#
# Prerequesites: have the following tools installed:
# - awscli
# - jq
# - session-manager-plugin (https://docs.aws.amazon.com/systems-manager/latest/userguide/session-manager-working-with-install-plugin.html)
#
# Usage: start_ssm_session <instance ID | IP | Name>
# Examples:
# start_ssm_session i-0041d4a4bd0fdcb2d
# start_ssm_session 10.0.103.41
# start_ssm_session "citus-worker-*"

export AWS_DEFAULT_OUTPUT="json"

start_ssm_session() {
  if [ -z "$1" ]; then
    echo "Instance name (wildcard accepted):"
    read -r NAME
  else
    NAME="$1"
  fi
  # searching by name
  INSTANCES=$(aws ec2 describe-instances  --filters "Name=tag:Name,Values=${NAME}" "Name=instance-state-name,Values=running" --query "Reservations[].Instances[].[InstanceId,Tags[?Key=='Name'].Value[] | [0]]")
  INSTANCE_COUNT=$(echo "$INSTANCES" | jq length)
  if [ "$INSTANCE_COUNT" -eq 0 ]; then
    # searching by internal IP
    INSTANCES=$(aws ec2 describe-instances  --filters "Name=private-ip-address,Values=${NAME}" "Name=instance-state-name,Values=running" --query "Reservations[].Instances[].[InstanceId,Tags[?Key=='Name'].Value[] | [0]]")
    INSTANCE_COUNT=$(echo "$INSTANCES" | jq length)
  fi
  if [ "$INSTANCE_COUNT" -eq 0 ]; then
    # searching by instance-id
    INSTANCES=$(aws ec2 describe-instances  --instance-ids "$NAME" --query "Reservations[].Instances[].[InstanceId,Tags[?Key=='Name'].Value[] | [0]]")
    INSTANCE_COUNT=$(echo "$INSTANCES" | jq length)
  fi

  if [ "$INSTANCE_COUNT" -eq 0 ]; then
    echo "Couldn't find any running instance with this name."
    return
  elif [ "$INSTANCE_COUNT" -gt 1 ]; then
    for ((i=0; i<$INSTANCE_COUNT; i++)); do
      ID=$(echo "$INSTANCES" | jq -r ".[$i][0]")
      NAME=$(echo "$INSTANCES" | jq -r ".[$i][1]")
      echo "[${i}] $ID - $NAME"
    done
    echo "Which one?"
    read INDEX
  else
    INDEX=0
  fi

  INSTANCE_ID=$(echo "$INSTANCES" | jq -r ".[$INDEX][0]")
  aws ssm start-session --target "$INSTANCE_ID"
}