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Fixes #12617 Change-Id: Ifc87b7d9cf699635087afb57febd01fb9a6d11b7 Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
110 lines
4.8 KiB
Markdown
110 lines
4.8 KiB
Markdown
# DERP
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This is the code for the [Tailscale DERP server](https://tailscale.com/kb/1232/derp-servers).
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In general, you should not need to or want to run this code. The overwhelming
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majority of Tailscale users (both individuals and companies) do not.
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In the happy path, Tailscale establishes direct connections between peers and
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data plane traffic flows directly between them, without using DERP for more than
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acting as a low bandwidth side channel to bootstrap the NAT traversal. If you
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find yourself wanting DERP for more bandwidth, the real problem is usually the
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network configuration of your Tailscale node(s), making sure that Tailscale can
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get direction connections via some mechanism.
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If you've decided or been advised to run your own `derper`, then read on.
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## Caveats
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* Node sharing and other cross-Tailnet features don't work when using custom
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DERP servers.
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* DERP servers only see encrypted WireGuard packets and thus are not useful for
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network-level debugging.
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* The Tailscale control plane does certain geo-level steering features and
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optimizations that are not available when using custom DERP servers.
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## Guide to running `cmd/derper`
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* You must build and update the `cmd/derper` binary yourself. There are no
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packages. Use `go install tailscale.com/cmd/derper@latest` with the latest
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version of Go. You should update this binary approximately as regularly as
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you update Tailscale nodes. If using `--verify-clients`, the `derper` binary
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and `tailscaled` binary on the machine must be built from the same git revision.
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(It might work otherwise, but they're developed and only tested together.)
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* The DERP protocol does a protocol switch inside TLS from HTTP to a custom
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bidirectional binary protocol. It is thus incompatible with many HTTP proxies.
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Do not put `derper` behind another HTTP proxy.
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* The `tailscaled` client does its own selection of the fastest/nearest DERP
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server based on latency measurements. Do not put `derper` behind a global load
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balancer.
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* DERP servers should ideally have both a static IPv4 and static IPv6 address.
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Both of those should be listed in the DERP map so the client doesn't need to
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rely on its DNS which might be broken and dependent on DERP to get back up.
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* A DERP server should not share an IP address with any other DERP server.
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* Avoid having multiple DERP nodes in a region. If you must, they all need to be
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meshed with each other and monitored. Having two one-node "regions" in the
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same datacenter is usually easier and more reliable than meshing, at the cost
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of more required connections from clients in some cases. If your clients
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aren't mobile (battery constrained), one node regions are definitely
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preferred. If you really need multiple nodes in a region for HA reasons, two
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is sufficient.
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* Monitor your DERP servers with [`cmd/derpprobe`](../derpprobe/).
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* If using `--verify-clients`, a `tailscaled` must be running alongside the
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`derper`, and all clients must be visible to the derper tailscaled in the ACL.
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* If using `--verify-clients`, a `tailscaled` must also be running alongside
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your `derpprobe`, and `derpprobe` needs to use `--derp-map=local`.
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* The firewall on the `derper` should permit TCP ports 80 and 443 and UDP port
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3478.
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* Only LetsEncrypt certs are rotated automatically. Other cert updates require a
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restart.
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* Don't use a firewall in front of `derper` that suppresses `RST`s upon
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receiving traffic to a dead or unknown connection.
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* Don't rate-limit UDP STUN packets.
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* Don't rate-limit outbound TCP traffic (only inbound).
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## Diagnostics
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This is not a complete guide on DERP diagnostics.
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Running your own DERP services requires exeprtise in multi-layer network and
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application diagnostics. As the DERP runs multiple protocols at multiple layers
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and is not a regular HTTP(s) server you will need expertise in correlative
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analysis to diagnose the most tricky problems. There is no "plain text" or
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"open" mode of operation for DERP.
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* The debug handler is accessible at URL path `/debug/`. It is only accessible
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over localhost or from a Tailscale IP address.
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* Go pprof can be accessed via the debug handler at `/debug/pprof/`
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* Prometheus compatible metrics can be gathered from the debug handler at
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`/debug/varz`.
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* `cmd/stunc` in the Tailscale repository provides a basic tool for diagnosing
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issues with STUN.
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* `cmd/derpprobe` provides a service for monitoring DERP cluster health.
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* `tailscale debug derp` and `tailscale netcheck` provide additional client
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driven diagnostic information for DERP communications.
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* Tailscale logs may provide insight for certain problems, such as if DERPs are
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unreachable or peers are regularly not reachable in their DERP home regions.
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There are many possible misconfiguration causes for these problems, but
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regular log entries are a good first indicator that there is a problem.
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