177 lines
8.9 KiB
Markdown
177 lines
8.9 KiB
Markdown
[](https://travis-ci.org/costela/wesher)
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[](https://goreportcard.com/report/github.com/costela/wesher)
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# wesher
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<img src="./dist/wesher.svg" width="300"/>
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`wesher` creates and manages an encrypted mesh overlay network across a group of nodes, using [wireguard](https://www.wireguard.com/).
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Its main use-case is adding low-maintenance security to public-cloud networks or connecting different cloud providers.
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**⚠ WARNING**: since mesh membership is controlled by a mesh-wide pre-shared key, this effectively downgrades some of the
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security benefits from wireguard. See [security considerations](#security-considerations) below for more details.
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## Quickstart
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0. Before starting:
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1. make sure the [wireguard](https://www.wireguard.com/) kernel module is installed on all nodes.
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2. The following ports must be accessible between all nodes (see [configuration options](#configuration-options) to change these):
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- 51820 UDP
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- 7946 UDP and TCP
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1. Download the latest release for your architecture (assuming `go` is installed):
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```
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$ wget -O wesher https://github.com/costela/wesher/releases/latest/download/wesher-$(go env GOARCH)
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$ chmod a+x wesher
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```
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2. On the first node:
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```
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# ./wesher
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```
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Running the command above on a terminal will currently output a generated cluster key as follows:
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```
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new cluster key generated: XXXXX
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```
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**Note**: the created key will only be shown if running on a terminal, to avoid keys leaking via logs.
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3. Lastly, on any further node:
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```
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# wesher --cluster-key XXXXX --join x.x.x.x
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```
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Where `XXXXX` is the base64 encoded 256 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.
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### Permissions
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Note that `wireguard` - and therefore `wesher` - need root access to work properly.
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It is also possible to give the `wesher` binary enough capabilities to manage the `wireguard` interface via:
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```
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# setcap cap_net_admin=eip wesher
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```
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This will enable running as an unprivileged user, but some functionality (like automatic adding peer entries to
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`/etc/hosts`; see [configuration options](#configuration-options) below) will not work.
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### (optional) systemd integration
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A minimal `systemd` unit file is provided under the `dist` folder and can be copied to `/etc/systemd/system`:
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```
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# wget -O /etc/systemd/system/wesher.service https://raw.githubusercontent.com/costela/wesher/master/dist/wesher.service
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# systemctl daemon-reload
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# systemctl enable wesher
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```
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The provided unit file assumes `wesher` is installed to `/usr/loca/sbin`.
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Note that, as mentioned above, the initial cluster key will not be displayed in the journal.
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It can either be initialized by running `wesher` manually once, or by pre-seeding via `/etc/default/wesher` as the `WESHER_CLUSTER_KEY` environment var (see [configuration options](#configuration-options) below).
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## Installing from source
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Alternatively, the latest `wesher` commit can be easily installed from sources:
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Preferred:
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```
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$ git clone https://github.com/costela/wesher.git
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$ make
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```
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Or:
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```
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$ GO111MODULE=on go get github.com/costela/wesher
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```
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*Note*: the latter will not provide a meaningful output for `--version`.
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## Features
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The `wesher` tool builds a cluster and manages the configuration of wireguard on each node to create peer-to-peer
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connections between all nodes, thus forming a full mesh VPN.
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This approach may not scale for hundreds of nodes (benchmarks accepted 😉), but is sufficiently performant to join
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several nodes across multiple cloud providers, or simply to secure inter-node comunication in a single public-cloud.
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### Automatic Key management
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The wireguard private keys are created on startup for each node and the respective public keys are then broadcast
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across the cluster.
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The control-plane cluster communication is secured with a pre-shared AES-256 key. This key can be be automatically
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created during startup of the first node in a cluster, or it can be provided (see [configuration](#configuration-options)).
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The cluster key must then be sent to other nodes via a out-of-band secure channel (e.g. ssh, cloud-init, etc).
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Once set, the cluster key is saved locally and reused on the next startup.
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### Automatic IP address management
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The overlay IP address of each node is automatically selected out of a private network (`10.0.0.0/8` by default; MUST be different from the underlying network used for cluster communication) and is consistently hashed based on the peer's hostname.
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The use of consistent hashing means a given node will always receive the same overlay IP address (see [limitations](#overlay-ip-collisions)
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of this approach below).
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**Note**: the node's hostname is also used by the underlying cluster management (using [memberlist](https://github.com/hashicorp/memberlist))
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to identify nodes and must therefore be unique in the cluster.
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### Automatic /etc/hosts management
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To ease intra-node communication, `wesher` also adds entries to `/etc/hosts` for each peer in the mesh. This enables using the nodes' hostnames to ensure communication over the secured overlay network (assuming `files` is the first entry for `hosts` in `/etc/nsswitch.conf`).
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See [configuration](#configuration-options) below for how to disable this behavior.
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### Seamless restarts
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If a node in the cluster is restarted, it will attempt to re-join the last-known nodes using the same cluster key.
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This means a restart requires no manual intervention.
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## Configuration options
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All options can be passed either as command-line flags or environment variables:
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| Option | Env | Description | Default |
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|---|---|---|---|
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| `--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 |
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| `--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 | |
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| `--init` | WESHER_INIT | whether to explicitly (re)initialize the cluster; any known state from previous runs will be forgotten | `false` |
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| `--bind-addr ADDR` | WESHER_BIND_ADDR | IP address to bind to for cluster membership (cannot be used with --bind-iface) | autodetected |
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| `--bind-iface IFACE` | WESHER_BIND_IFACE | Interface to bind to for cluster membership (cannot be used with --bind-addr)| |
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| `--cluster-port PORT` | WESHER_CLUSTER_PORT | port used for membership gossip traffic (both TCP and UDP); must be the same across cluster | `7946` |
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| `--wireguard-port PORT` | WESHER_WIREGUARD_PORT | port used for wireguard traffic (UDP); must be the same across cluster | `51820` |
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| `--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` |
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| `--interface DEV` | WESHER_INTERFACE | name of the wireguard interface to create and manage | `wgoverlay` |
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| `--no-etc-hosts` | WESHER_NO_ETC_HOSTS | whether to skip writing hosts entries for each node in mesh | `false` |
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| `--log-level LEVEL` | WESHER_LOG_LEVEL | set the verbosity (one of debug/info/warn/error) | `warn` |
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## Security considerations
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The decision of whom to allow in the mesh is made by [memberlist](https://github.com/hashicorp/memberlist) and is secured by a
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cluster-wide pre-shared key.
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Compromise of this key will allow an attacker to:
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- access services exposed on the overlay network
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- impersonate and/or disrupt traffic to/from other nodes
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It will not, however, allow the attacker access to decrypt the traffic between other nodes.
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This pre-shared key is currently static, set up during cluster bootstrapping, but will - in a future version - be
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rotated for improved security.
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## Current known limitations
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### Overlay IP collisions
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Since the assignment of IPs on the overlay network is currently decided by the individual node and implemented as a
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naive hashing of the hostname, there can be no guarantee two hosts will not generate the same overlay IPs.
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This limitation may be worked around in a future version.
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### Split-brain
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Once a cluster is joined, there is currently no way to distinguish a failed node from an intentionally removed one.
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This is partially by design: growing and shrinking your cluster dynamically (e.g. via autoscaling) should be as easy
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as possible.
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However, this does mean longer connection loss between any two parts of the cluster (e.g. across a WAN link between
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different cloud providers) can lead to a split-brain scenario where each side thinks the other side is simply "gone".
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There is currently no clean solution for this problem, but one could work around it by designating edge nodes which
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periodically restart `wesher` with the `--join` option pointing to the other side.
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Future versions might include the notion of a "static" node to more cleanly avoid this.
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