Building a Cloud in the Cloud: Running Apache CloudStack on Amazon EC2, Part 1

This blog is written by Mark Rogers, SDE II – Customer Engineering Amazon Web Services .

How do you put a cloud inside another cloud? Some features that make Amazon Elastic Compute Cloud (Amazon EC2) secure and wonderful also make running CloudStack difficult. The biggest obstacle is that Amazon Web Services and CloudStack both want to manage network resources. Therefore, we must keep them out of each other’s way. This requires some steps that aren’t obvious, and it took a long time to figure out. I’m going to share what I learned, so that you can navigate the process more easily.

Apache CloudStack is an open-source platform for deploying and managing virtual machines (VMs) and the associated network and storage infrastructure. You would normally run it on your own hardware to create your own cloud. But there can be advantages to running it inside of an Amazon Virtual Private Cloud (Amazon VPC) , including how it could help you migrate out of a data center. It’s a great way to create disposable environments for experiments or training. Furthermore, it’s a convenient way to test-drive the new CloudStack support in Amazon Elastic Kubernetes Service (Amazon EKS) Anywhere . In my case, I needed to create development and test environments for a project that uses the CloudStack API. The environments needed to be shared and scalable. Our build pipelines were already in Amazon Web Services, so it made sense to put the new environments there, too.

CloudStack can work with a number of hypervisors. The instructions in this article will use Kernel-based Virtual Machine (KVM) on Linux. KVM will manage the VMs at a low level, and CloudStack will manage KVM.

Prerequisites

Most of the information in this article should be applicable to a range of CloudStack versions. I targeted CloudStack 4.14 on CentOS 7. I also tested CloudStack versions 4.16 and 4.17, and I recommend them.

The official CentOS 7 x86_64 HVM image works well. If you use a different Linux flavor or version, then you might have to modify some of the implementation details.

You’ll need to know the basics of CloudStack. The scope of this article is making CloudStack and Amazon Web Services coexist peacefully. Once CloudStack is running, I’m assuming that you’ll handle things from there. Refer to the Amazon Web Services documentation and CloudStack documentation for information on security and other best practices.

Making things easier

I wrote some scripts to automate the installation. You can run them on EC2 instances with CentOS 7, and they’ll do all the installation and OS configuration for you. You can use them as they are, or customize them to meet your needs. I also wrote some Amazon Web Services CloudFormation templates you can copy in order to create a demo environment. The README file has more details.

Amazon EC2 instance types

KVM requires hardware virtualization support . Most EC2 instances are VMs that don’t support nested virtualization. To get access to the bare hardware, you need a metal instance type .

I like c5.metal because it’s one of the least expensive metal types, and has a low cost per vCPU. It has 96 vCPUs and 192 GiB of memory. If you run 20 VMs on it, with 4 CPU cores and 8 GiB of memory each, then you’d still have 16 vCPUs and 32 GiB to share between the operating system, CloudStack, and MySQL. Using CloudStack’s overprovisioning feature, you could fit even more VMs if they’re running light loads.

Networking

The biggest challenge is the network. Amazon Web Services knows which IP and MAC addresses should exist, and it knows the machines to which they should belong. It blocks any traffic that doesn’t fit its idea of how the network should behave. Simultaneously, CloudStack assumes that any IP or MAC address it invents should work just fine. When CloudStack assigns addresses to VMs on an Amazon Web Services subnet, their network traffic gets blocked.

You could get around this by enabling network address translation (NAT) on the instance running CloudStack. That’s a great solution if it fits your needs, but it makes it hard for other machines in your Amazon VPC to contact your VMs. I recommend a different approach.

Although Amazon Web Services restricts what you can do with its layer 2 network, it’s perfectly happy to let you run your own layer 3 router. Your EC2 instance can act as a router to a new virtual subnet that’s outside of the jurisdiction of Amazon Web Services. The instance integrates with Amazon Web Services just like a VPN appliance, routing traffic to wherever it needs to go. CloudStack can do whatever it wants in the virtual subnet, and everybody’s happy.

What do I mean by a virtual subnet? This is a subnet that exists only inside the EC2 instance. It consists of logical network interfaces attached to a Linux bridge. The entire subnet exists inside a single EC2 instance. It doesn’t scale well, but it’s simple. In my next post, I’ll cover a more complicated setup with an overlay network that spans multiple instances to allow horizontal scaling.

The simple way

The simple way is to put everything in one EC2 instance, including the database, file storage, and a virtual subnet. Because everything’s stored locally, allocate enough disk space for your needs. 500 GB will be enough to support a few basic VMs. Create or select a security group for your instance that gives users access to the CloudStack UI (TCP port 8080). The security group should also allow access to any services that you’ll offer from your VMs.

EC2 instance summary info showing 1 instance, CentOS 7 (x86_64) AMI, c5.metal instance type, a security group name, and a 500 GiB volume

When you have your instance, configure Amazon Web Services to treat it as a router.

Go to Amazon EC2 in the Amazon Web Services Management Console .
Select your instance, and stop source/destination checking .

In the EC2 Actions menu, select Networking, then Change source/destination check.

3. Update the subnet route tables .

a. Go to the VPC settings, and select Route Tables.

b. Identify the tables for subnets that need CloudStack access.

c. In each of these tables, add a route to the new virtual subnet. The route target should be your EC2 instance.

4. Depending on your network needs, you may also need to add routes to transit gateways, VPN endpoints, etc.

Because everything will be on one server, creating a virtual subnet is simply a matter of creating a Linux bridge. CloudStack must find a network adapter attached to the bridge. Therefore, add a dummy interface with a name that CloudStack will recognize .

A single EC2 instance contains the CloudStack management service, the CloudStack agent, a dummy network interface, several virtual machines, and a router. All of those things are connected to each other by a virtual subnet that exists inside the instance. The instance's elastic network interface is connected between the router and the Amazon VPC. The following snippet shows how I configure networking in CentOS 7. You must provide values for the variables $virutal_host_ip_address and $virtual_netmask to reflect the virtual subnet that you want to create. For $dns_address, I recommend the base of the VPC IPv4 network range, plus two . You shouldn’t use 169.654.169.253 because CloudStack reserves link-local addresses for its own use.

yum install -y bridge-utils net-tools

# The bridge must be named cloudbr0.

cat << EOF > /etc/sysconfig/network-scripts/ifcfg-cloudbr0
DEVICE=cloudbr0
TYPE=Bridge
ONBOOT=yes
BOOTPROTO=none
IPV6INIT=no
IPV6_AUTOCONF=no
DELAY=5
STP=yes
USERCTL=no
NM_CONTROLLED=no
IPADDR=$virtual_host_ip_address
NETMASK=$virtual_netmask
DNS1=$dns_address
EOF

# Create a dummy network interface.
cat << EOF > /etc/sysconfig/modules/dummy.modules
#!/bin/sh
/sbin/modprobe dummy numdummies=1
/sbin/ip link set name ethdummy0 dev dummy0
EOF

chmod +x /etc/sysconfig/modules/dummy.modules
/etc/sysconfig/modules/dummy.modules

cat << EOF > /etc/sysconfig/network-scripts/ifcfg-ethdummy0
TYPE=Ethernet
BOOTPROTO=none
NAME=ethdummy0
DEVICE=ethdummy0
ONBOOT=yes
BRIDGE=cloudbr0
NM_CONTROLLED=no
EOF

# Turn the instance into a router

echo 'net.ipv4.ip_forward=1' >> /etc/sysctl.conf
sysctl -p

# Must kill dhclient or the network service won't restart properly.
# A reboot would also work, if you’d rather do that.

pkill dhclient
systemctl restart network

CloudStack must know which IP addresses to use for inter-service communication. It will select by resolving the machine’s fully qualified domain name (FQDN) to an address. The following commands will make it to choose the right one. You must provide a value for $virtual_host_ip_address.

hostnamectl set-hostname cloudstack.localdomain

echo "$virtual_host_ip_address cloudstack.localdomain" >> 
/etc/hosts

You can finish the setup by following the Quick Installation Guide .

Remember that CloudStack is only directly connected to your virtual network. The EC2 instance is the router that connects the virtual subnet to the Amazon VPC. When you’re configuring CloudStack, use your instance’s virtual subnet address as the default gateway.

Use the EC2 instance's virtual subnet IP address as the default gateway in CloudStack. In this example, the virtual subnet is 10.100.0.0/16, and the instance's address in that subnet is 10.100.0.1. CloudStack then uses 10.100.0.1 as the default gateway.

To access CloudStack from your workstation, you’ll need a connection to your VPC. This can be through a client VPN or a bastion host . If you use a bastion, its subnet needs a route to your virtual subnet, and you’ll need an SSH tunnel for your browser to access the CloudStack UI. The UI is at http://x.x.x.x:8080/client/, where x.x.x.x is your CloudStack instance’s virtual subnet address. Note that CloudStack’s console viewer won’t work if you’re using an SSH tunnel.

If you’re just experimenting with CloudStack, then I suggest saving money by stopping your instance when it isn’t needed. The safe way to do that is:

Disable your zone in the CloudStack UI.
Put the primary storage into maintenance mode.
Wait for the switch to maintenance mode to be complete.
Stop the EC2 instance.

When you’re ready to turn everything back on, simply reverse those steps. If you have any virtual routers in CloudStack, then you may need to start those, too.

Cleanup

If you used my CloudFormation template, then delete the stack and remove any route table entries you added. If you didn’t use CloudFormation, then terminate the EC2 instance , delete the security group you created for it, and remove any route table entries that you added.

Conclusion

Getting CloudStack to run on Amazon Web Services isn’t so bad. The hardest part is simply knowing how. The setup explained here is great for small installations, but it can only scale vertically. In my next post, I’ll show you how to create an installation that scales horizontally. Instead of using a virtual subnet that exists in a single EC2 instance, we’ll build an overlay network that spans multiple instances. It will use more components and features, including some that might be new to you. I hope you find it interesting!

Now that you can create a simple setup, give it a try! I hope you have fun and learn something new along the way. Comment with the results of your experiments.

“Apache”, “Apache CloudStack”, and “CloudStack” are trademarks of the Apache Software Foundation.