diff --git a/src/aws/up.sh b/src/aws/up.sh
index 10f46b42..f50a2681 100644
--- a/src/aws/up.sh
+++ b/src/aws/up.sh
@@ -10,175 +10,189 @@ groupName=luftballons-sg
 instanceName=luftballon
 checkSSH=~/.ssh/$publickey
 
+checkSshKey() {
+  aws ec2 describe-key-pairs --key-names $keyname &> /dev/null
+  return $?
+}
+
+checkSecurityGroup() {
+  aws ec2 describe-security-groups --group-names $groupName &> /dev/null
+  return $?
+}
 
+checkInstance() {
+  aws ec2 describe-instances --filters "Name=tag:Name,Values=$instanceName" --query "Reservations[*].Instances[*].InstanceId" --output text
+}
+
+checkInstanceState() {
+  ID=$1
+  aws ec2 describe-instances --instance-ids $ID --query "Reservations[*].Instances[*].State.Name" --output text
+}
 
 function importSshKey()
 {
-    if [[ -f ~/.ssh/$publickey ]]
-    then
-        aws ec2 import-key-pair --key-name "$keyname" --public-key-material fileb://~/.ssh/$publickey  
-    else
-        echo 'ssh key pair (~/.ssh/$publickey) do not exist ~/.ssh/$publickey'
-        echo 'Please generate the ssh key by the commad "ssh-keygen -t rsa"'
-        exit 1
-    fi
+  if [[ -f ~/.ssh/$publickey ]]; then
+    aws ec2 import-key-pair --key-name "$keyname" --public-key-material fileb://~/.ssh/$publickey  
+  else
+    echo 'ssh key pair (~/.ssh/$publickey) do not exist ~/.ssh/$publickey'
+    echo 'Please generate the ssh key by the commad "ssh-keygen -t rsa"'
+    exit 1
+  fi
 }
 
 function addPort(){
-	aws ec2 authorize-security-group-ingress \
-		--group-name $groupName \
-		--protocol tcp \
-		--port $1 \
-		--cidr 0.0.0.0/0
+  aws ec2 authorize-security-group-ingress \
+    --group-name $groupName \
+    --protocol tcp \
+    --port $1 \
+    --cidr 0.0.0.0/0
 }
 
 function addUDPPort() {
-	aws ec2 authorize-security-group-ingress \
-		--group-name $groupName \
-		--protocol udp \
-		--port $1 \
-		--cidr 0.0.0.0/0
+  aws ec2 authorize-security-group-ingress \
+    --group-name $groupName \
+    --protocol udp \
+    --port $1 \
+    --cidr 0.0.0.0/0
 }
 
-
 function createSecurityGroups(){
-	aws ec2 create-security-group \
-		--group-name $groupName \
-		--description "luftballons security group"
-
-	if [ -z "$portConfigArray" ]
-	then
-		portConfigArray="8080:80,8443:443,2022:22"
-	fi
-
-    portArray=($(makePortArray "$portConfigArray"))
-
-	for i in "${portArray[@]}"
-	do
-		addPort $i
-		echo $i
-	done
-
-	if [ -z "$udpPortConfigArray" ]
-	then
-		udpPortConfigArray="1194"
-	fi
-
-    portArray=($udpPortConfigArray)
-
-	for i in "${portArray[@]}"
-	do
-		addUDPPort $i
-		echo $i
-	done
+  aws ec2 create-security-group \
+    --group-name $groupName \
+    --description "luftballons security group"
+  if [ -z "$portConfigArray" ]; then
+    portConfigArray="8080:80,8443:443,2022:22"
+  fi
+  portArray=($(makePortArray "$portConfigArray"))
+  for i in "${portArray[@]}"; do
+    addPort $i
+    echo $i
+  done
+  if [ -z "$udpPortConfigArray" ]; then
+    udpPortConfigArray="1194"
+  fi
+  portArray=($udpPortConfigArray)
+  for i in "${portArray[@]}"; do
+    addUDPPort $i
+    echo $i
+  done
 }
 
 function createEc2(){
-    image="ami-0750fb43a63427eff"
-    #image="ami-01e5ff16fd6e8c542"
-	aws ec2 run-instances \
-		--count 1 \
-		--image-id $image \
-		--instance-type t2.micro \
-		--key-name $keyname \
-		--security-groups $groupName 
+  image="ami-0750fb43a63427eff"
+  #image="ami-01e5ff16fd6e8c542"
+  aws ec2 run-instances \
+    --count 1 \
+    --image-id $image \
+    --instance-type t2.micro \
+    --key-name $keyname \
+    --security-groups $groupName 
 }
 
 function findData(){
-	keyWord=$1
-	grep $keyWord | awk -F':' '{ print $2 }' | sed 's/ //g; s/"//g; s/,//g' 
+  keyWord=$1
+  grep $keyWord | awk -F':' '{ print $2 }' | sed 's/ //g; s/"//g; s/,//g' 
 }
 
 function deleteKeyword(){
-	keyWord=$1
-    sed "s/$keyWord//g; s/ //g"
+  keyWord=$1
+  sed "s/$keyWord//g; s/ //g"
 }
 
 function getValueByKeyword(){
-	keyWord=$1
-    findData $keyWord | deleteKeyword $keyWord
+  keyWord=$1
+  findData $keyWord | deleteKeyword $keyWord
 }
 
 function usage {
-		echo "script usage: $(basename \$0 aws up) [-n ssh key name] [-p] [-a change key name, instance name, and group name]" >&2
-        echo 'Start Luftballon.'
-        echo '   -n          Change SSH key name on AWS'
-        echo '   -a          Change SSH key name, instance name, and group name'
-        echo '   -p          Use stored port Numbers instead of the default port number.'
-        exit 1
+  echo "script usage: $(basename \$0 aws up) [-n ssh key name] [-p] [-a change key name, instance name, and group name]" >&2
+  echo 'Start Luftballon.'
+  echo '   -n          Change SSH key name on AWS'
+  echo '   -a          Change SSH key name, instance name, and group name'
+  echo '   -p          Use stored port Numbers instead of the default port number.'
+  exit 1
 }
 
 function up {
-	while getopts 'n:pN:a:' OPTION; do
-	case "$OPTION" in
-		n)
-		keyname=$OPTARG
-		;;
-		p)
-		portConfigArray=$(getArrayValueAsStringByKey $instanceName tcpPortArray)
-		udpPortConfigArray=$(getArrayValueAsStringByKey $instanceName udpPortArray)
-		if [ -z "$portConfigArray" ]
-		then
-			echo "There is no stored port numbers. The default port numbers are used"
-		fi
-		if [ -z "$udpPortConfigArray" ]
-		then
-			echo "There is no stored udp port numbers. The default port numbers are used"
-		fi
-		;;
-		a)
-		groupName=$OPTARG-sg
-		instanceName=$OPTARG
-		keyname=$OPTARG
-		;;
-		?)
-		usage
-		;;
-	esac
-	done
-	shift "$(($OPTIND -1))"
-
-	aws --version || ( echo "Run './installAwsCli.sh' first. AWS CLI is not installed." && exit 1 )
-
-	if test ! -f "$checkSSH"; then
-		echo "Run 'ssh-keygen' first, with an empty passphrase for no passphrase. Missing ssh key." && exit 1
-	fi
-
-	if [ -z $keyname ]
-	then
-		keyname=luftballon
-	fi
-
-
-	keyName=$(importSshKey | getValueByKeyword KeyName )
-
-	if [ -z $keyName ]
-	then 
-		exit 1
-	fi
-
-	echo "Success to add ssh key: $keyName"
-
-	createSecurityGroups
-	echo "Add security group"
-
-	instanceId=$(createEc2 | getValueByKeyword InstanceId )
-	echo "Create EC2 Instance"
-	echo "Instance id is $instanceId"
-
-
-	aws ec2 create-tags --resources $instanceId --tags Key=Name,Value=$instanceName
-	aws ec2 create-tags --resources $instanceId --tags Key=Class,Value=treehouses
-
-
-	publicIp=$(waitForOutput "getLatestIpAddress $instanceId")
-	echo "Public IP Address is $publicIp"
-
-	echo "Will open ssh tunnel soon"
-	isOpen=$(waitForOutput "ssh-keyscan -H $publicIp | grep ecdsa-sha2-nistp256")
-	echo "Opened ssh tunnel"
-
-	openSSHTunnel $instanceName $publicIp $portConfigArray
-
-	storeConfigIntoTreehousesConfigAsStringfiedJson $instanceName $keyName $instanceId $publicIp $groupName
+  while getopts 'n:pN:a:' OPTION; do
+    case "$OPTION" in
+      n)
+        keyname=$OPTARG
+        ;;
+      p)
+        portConfigArray=$(getArrayValueAsStringByKey $instanceName tcpPortArray)
+        udpPortConfigArray=$(getArrayValueAsStringByKey $instanceName udpPortArray)
+        if [ -z "$portConfigArray" ]; then
+          echo "There is no stored port numbers. The default port numbers are used"
+        fi
+        if [ -z "$udpPortConfigArray" ]; then
+          echo "There is no stored udp port numbers. The default port numbers are used"
+        fi
+        ;;
+      a)
+        groupName=$OPTARG-sg
+        instanceName=$OPTARG
+        keyname=$OPTARG
+        ;;
+      ?)
+        usage
+	;;
+      esac
+    done
+    shift "$(($OPTIND -1))"
+
+    aws --version || ( echo "Run './installAwsCli.sh' first. AWS CLI is not installed." && exit 1 )
+
+    if test ! -f "$checkSSH"; then
+      echo "Run 'ssh-keygen' first, with an empty passphrase for no passphrase. Missing ssh key." && exit 1
+    fi
+
+    if [ -z $keyname ]; then
+      keyname=luftballon
+    fi
+
+    if ! checkSshKey ; then
+      importedKeyName=$(importSshKey | getValueByKeyword KeyName )
+      if [ -z $importedKeyName ]; then 
+        exit 1
+      fi
+      echo "Success to add ssh key: $importedKeyName"
+    else
+      echo "The key pair $keyname already exists. Please use another key name."
+    fi
+
+    if ! checkSecurityGroup; then
+      createSecurityGroups
+      echo "Add security group"
+      # Add rules to Security Group as needed
+    else
+      echo "Security Group already exists."
+    fi
+
+    instanceId=$(checkInstance)
+    if [ -z "$instanceId" ]; then
+      instanceState=""
+      instanceId=$(createEc2 | getValueByKeyword InstanceId)
+      echo "Creating and running EC2 instance..."
+      echo "Instance id is $instanceId"
+      aws ec2 create-tags --resources $instanceId --tags Key=Name,Value=$instanceName
+      aws ec2 create-tags --resources $instanceId --tags Key=Class,Value=treehouses
+      publicIp=$(waitForOutput "getLatestIpAddress $instanceId")
+      echo "Public IP Address is $publicIp"
+      echo "Will open ssh tunnel soon"
+      isOpen=$(waitForOutput "ssh-keyscan -H $publicIp | grep ecdsa-sha2-nistp256")
+      echo "Opened ssh tunnel"
+      openSSHTunnel $instanceName $publicIp $portConfigArray
+      storeConfigIntoTreehousesConfigAsStringfiedJson $instanceName $importedKeyName $instanceId $publicIp $groupNameaws ec2 create-tags --resources $instanceId --tags Key=Class,Value=treehouses
+    else
+      instanceState=$(checkInstanceState $instanceId)
+    if [ "$instanceState" = "running" ]; then
+      echo "EC2 instance is already running."
+    elif [ "$instanceState" = "stopped" ]; then
+      echo "Starting stopped EC2 instance..."
+      start $instanceName
+    else
+      echo "EC2 instance is in state: $instanceState."
+    fi
+  fi
 }