127 lines
6.6 KiB
Markdown
127 lines
6.6 KiB
Markdown
[](https://travis-ci.org/costela/wesher)
|
|
[](https://goreportcard.com/report/github.com/costela/wesher)
|
|
|
|
# wesher
|
|
|
|
`wesher` creates and manages a mesh overlay network across a group of nodes, using [wireguard](https://www.wireguard.com/).
|
|
|
|
Its main use-case is adding low-maintenance security to public-cloud networks or connecting different cloud providers.
|
|
|
|
**⚠ WARNING**: since mesh membership is controlled by a mesh-wide pre-shared key, this effectively downgrades some of the
|
|
security benefits from wireguard. See [security considerations](#security-considerations) below for more details.
|
|
|
|
## Quickstart
|
|
|
|
Before starting, make sure [wireguard](https://www.wireguard.com/) is installed on all nodes.
|
|
|
|
The following ports must be accessible between all nodes (see [configuration options](#configuration-options) to change these):
|
|
- 51820 UDP
|
|
- 7946 UDP and TCP
|
|
|
|
Install `wesher` on all nodes with go >= 1.11:
|
|
```
|
|
$ GO111MODULE=on go get github.com/costela/wesher
|
|
```
|
|
|
|
On the first node (assuming `$GOPATH/bin` is in the `$PATH`):
|
|
```
|
|
# wesher
|
|
```
|
|
|
|
Running the command above on a terminal will currently output a generated cluster key, like:
|
|
```
|
|
new cluster key generated: XXXXX
|
|
```
|
|
|
|
Then, on any further node:
|
|
```
|
|
# wesher --cluster-key XXXXX --join x.x.x.x
|
|
```
|
|
|
|
Where `XXXXX` is the base64 encoded 32 bit key printed by the step above and `x.x.x.x` is the hostname or IP of any of
|
|
the nodes already joined to the mesh cluster.
|
|
|
|
*Note*: `wireguard` - and therefore `wesher` - need root access.
|
|
|
|
## Features
|
|
|
|
The `wesher` tool builds a cluster and manages the configuration of wireguard on each node to create peer-to-peer
|
|
connections between all nodes, thus forming a full mesh VPN.
|
|
This approach may not scale for hundreds of nodes (benchmarks accepted 😉), but is sufficiently performant to join
|
|
several nodes across multiple cloud providers, or simply to secure inter-node comunication in a single public-cloud.
|
|
|
|
### Automatic Key management
|
|
|
|
The wireguard private keys are created on startup for each node and the respective public keys are then broadcast
|
|
across the cluster.
|
|
|
|
The control-plane cluster communication is secured with a pre-shared AES-256 bit key. This key can be be automatically
|
|
created during startup of the first node in a cluster, or it can be provided (see [configuration](#configuration-options)).
|
|
The cluster key must then be sent to other nodes via a out-of-band secure channel (e.g. ssh, cloud-init, etc).
|
|
Once set, the cluster key is saved locally and reused on the next startup.
|
|
|
|
### Automatic IP address management
|
|
|
|
The overlay IP address of each node is selected out of a private network (`10.0.0.0/8` by default) and is consistently
|
|
hashed based on the hostname, meaning a host will always receive the same overlay IP address (see [limitations](#overlay-ip-collisions)
|
|
of this approach below). The hostname is also used by the underlying cluster management (using [memberlist](https://github.com/hashicorp/memberlist))
|
|
to identify nodes and must therefore be unique in the cluster.
|
|
|
|
To ease intra-node communication, `wesher` also adds entries to `/etc/hosts` for each other node. See [configuration](#configuration-options)
|
|
below for how to disable this behavior.
|
|
|
|
### Restoring state
|
|
|
|
If a node in the cluster is restarted, it will attempt to re-join the last-known nodes using the same cluster key.
|
|
This means a restart requires no manual intervention.
|
|
|
|
## Configuration options
|
|
|
|
All options can be passed either as command-line flags or environment variables:
|
|
|
|
| Option | Env | Description | Default |
|
|
|---|---|---|---|
|
|
| `--cluster-key KEY` | WESHER_CLUSTER_KEY | shared key for cluster membership; must be 32 bytes base64 encoded; will be generated if not provided | autogenerated/loaded |
|
|
| `--join HOST,...` | WESHER_JOIN | comma separated list of hostnames or IP addresses to existing cluster members; if not provided, will attempt resuming any known state or otherwise wait for further members | |
|
|
| `--bind-addr ADDR` | WESHER_BIND_ADDR | IP address to bind to for cluster membership | autodetected |
|
|
| `--cluster-port PORT` | WESHER_CLUSTER_PORT | port used for membership gossip traffic (both TCP and UDP); must be the same across cluster | `7946` |
|
|
| `--wireguard-port PORT` | WESHER_WIREGUARD_PORT | port used for wireguard traffic (UDP); must be the same across cluster | `51820` |
|
|
| `--overlay-net ADDR/MASK` | WESHER_OVERLAY_NET | the network in which to allocate addresses for the overlay mesh network (CIDR format); smaller networks increase the chance of IP collision | `10.0.0.0/8` |
|
|
| `--interface DEV` | WESHER_INTERFACE | name of the wireguard interface to create and manage | `wgoverlay` |
|
|
| `--no-etc-hosts` | WESHER_NO_ETC_HOSTS | whether to skip writing hosts entries for each node in mesh | `false` |
|
|
| `--log-level LEVEL` | WESHER_LOG_LEVEL | set the verbosity (one of debug/info/warn/error) | `warn` |
|
|
|
|
|
|
## Security considerations
|
|
|
|
The decision of whom to allow in the mesh is made by [memberlist](https://github.com/hashicorp/memberlist) and is secured by a
|
|
cluster-wide pre-shared key.
|
|
Compromise of this key will allow an attacker to:
|
|
- access services exposed on the overlay network
|
|
- impersonate and/or disrupt traffic to/from other nodes
|
|
It will not, however, allow the attacker access to decrypt the traffic between other nodes.
|
|
|
|
This pre-shared key is currently static, set up during cluster bootstrapping, but will - in a future version - be
|
|
rotated for improved security.
|
|
|
|
## Current known limitations
|
|
|
|
### Overlay IP collisions
|
|
|
|
Since the assignment of IPs on the overlay network is currently decided by the individual node and implemented as a
|
|
naive hashing of the hostname, there can be no guarantee two hosts will not generate the same overlay IPs.
|
|
This limitation may be worked around in a future version.
|
|
|
|
### Split-brain
|
|
|
|
Once a cluster is joined, there is currently no way to distinguish a failed node from an intentionally removed one.
|
|
This is partially by design: growing and shrinking your cluster dynamically (e.g. via autoscaling) should be as easy
|
|
as possible.
|
|
|
|
However, this does mean longer connection loss between any two parts of the cluster (e.g. across a WAN link between
|
|
different cloud providers) can lead to a split-brain scenario where each side thinks the other side is simply "gone".
|
|
|
|
There is currently no clean solution for this problem, but one could work around it by designating edge nodes which
|
|
periodically restart `wesher` with the `--join` option pointing to the other side.
|
|
Future versions might include the notion of a "static" node to more cleanly avoid this.
|