mirror of
https://github.com/threefoldtech/mycelium.git
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Lee Smet
99 lines
2.6 KiB
Markdown
99 lines
2.6 KiB
Markdown
# Vsock transport
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Mycelium supports [VM sockets (vsock)](https://man7.org/linux/man-pages/man7/vsock.7.html) as a
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transport, allowing a mycelium node running inside a virtual machine to peer directly with a node
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running on the hypervisor host (or vice versa), without requiring a network interface.
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Vsock is only available on Linux.
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## How it works
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Vsock addresses a device by its **Context ID (CID)** and a **port number**, rather than an IP
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address. Key CID values:
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| CID | Meaning |
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|-----|---------|
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| `2` | The hypervisor host |
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| `3` and up | Guest VMs (assigned by the hypervisor) |
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| `4294967295` | Any CID (used when listening) |
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A node that wants to accept inbound vsock connections binds to `VMADDR_CID_ANY` on a given port.
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The connecting side targets the peer's CID explicitly.
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## Starting a node with a vsock listener
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Pass `--vsock-listen-port` when starting `mycelium` to accept inbound vsock connections:
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```sh
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mycelium --vsock-listen-port 9651
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```
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The listener binds on all CIDs (`VMADDR_CID_ANY`), so both host-to-guest and guest-to-host
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connections are accepted on the same port.
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## Connecting to a peer over vsock
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Vsock peers are specified with the `vsock://` scheme in the endpoint format:
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```
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vsock://<CID>:<port>
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```
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### Example: guest VM connecting to the host
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On the **host**, start mycelium with a vsock listener:
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```sh
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mycelium --vsock-listen-port 9651
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```
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On the **guest VM**, connect to the host (CID `2`) as a static peer:
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```sh
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mycelium --peers vsock://2:9651
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```
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### Example: host connecting to a guest VM
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Find the guest's CID by consulting your hypervisor's documentation.
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On the **guest**, start mycelium with a vsock listener:
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```sh
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mycelium --vsock-listen-port 9651
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```
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On the **host**, connect to the guest using its CID (e.g. `42`):
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```sh
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mycelium --peers vsock://42:9651
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```
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## Configuration file
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Vsock settings can also be placed in the mycelium configuration file:
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```toml
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# Listen for inbound vsock connections on this port
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vsock_listen_port = 9651
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# Connect to the hypervisor host as a static peer
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peers = ["vsock://2:9651"]
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```
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## Combining vsock with other transports
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Vsock and IP-based transports can be used simultaneously. A node can listen on
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both TCP and vsock at the same time, and peer over both:
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```sh
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mycelium --tcp-listen-port 9651 --vsock-listen-port 9651 --peers vsock://2:9651
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```
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## Link cost
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The vsock transport is assigned a lower link cost than any IP-based transport,
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reflecting that it is a local virtual channel with negligible latency. Mycelium
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will prefer a vsock path over an IP path when both are available to the same
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destination.
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