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Cloud platforms

Generally, running strongSwan on a cloud platform is relatively painless,
because only the hardware is virtualized. The kernel- and userspace is untouched.

General Warnings And Problems

Generally, in a cloud environment, the underlying network checks the source IP address
of the sent IP packets. You need to be able to deactivate this check in order
to use strongSwan as a VPN gateway, either in a roadwarrior or a site-to-site scenario, except
if you masquerade the source address of all packets that are transmitted over the network.
It is advisable to avoid NAT though at any cost, because it prevents you from
adressing remote endpoints.
This only applies to the outermost IP packet though, so it does not pertain
the inner IP packet of any tunneling protocol.

As an alternative, the packets from and to the VPN gateway can be transported to
the hosts on the local network using other means than directly on top of Ethernet,
like by using IPsec in tunnel mode, GRE, IPinIP or other protocols.

Container Virtualization

Container virtualized environments often do not offer a working IPsec stack to
software in the container. Therefore, kernel-libipsec has to be used instead.
To use kernel-libipsec, tun devices have to be available. Keep in mind that using
kernel-libipsec has drawbacks and is generally discouraged. Change to a hardware
virtualized virtual machine, if possible.
OpenVZ uses container virtualization.
Virtuozzo can also be a container. With Virtuozzo, it depends on the VM type.
If charon complains about not being able to find a usable IPsec stack, then it's very likely container virtualized.
strongSwan in a docker container works with kernel a kernel IPsec, if the host operating system has a working IPsec
stack and if the docker container, as well as strongSwan have the necessary privileges to access it (CAP_NET_ADMIN).
You do not have to enable host networking.

AWS EC2

On AWS, the source check of a machine can be disabled in the EC2 management menu.
An article with more information can be found here.

Google Cloud Engine

No specialties about GCE are known at this point.

DigitalOcean Droplets

On DigitalOcean, the source check can not be disabled.