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tailscale/ipn/ipnlocal
Brad Fitzpatrick 88c2afd1e3 ipn/ipnlocal, net/dns*, util/cloudenv: specialize DNS config on Google Cloud
This does three things:

* If you're on GCP, it adds a *.internal DNS split route to the
  metadata server, so we never break GCP DNS names. This lets people
  have some Tailscale nodes on GCP and some not (e.g. laptops at home)
  without having to add a Tailnet-wide *.internal DNS route.
  If you already have such a route, though, it won't overwrite it.

* If the 100.100.100.100 DNS forwarder has nowhere to forward to,
  it forwards it to the GCP metadata IP, which forwards to 8.8.8.8.
  This means there are never errNoUpstreams ("upstream nameservers not set")
  errors on GCP due to e.g. mangled /etc/resolv.conf (GCP default VMs
  don't have systemd-resolved, so it's likely a DNS supremacy fight)

* makes the DNS fallback mechanism use the GCP metadata IP as a
  fallback before our hosted HTTP-based fallbacks

I created a default GCP VM from their web wizard. It has no
systemd-resolved.

I then made its /etc/resolv.conf be empty and deleted its GCP
hostnames in /etc/hosts.

I then logged in to a tailnet with no global DNS settings.

With this, tailscaled writes /etc/resolv.conf (direct mode, as no
systemd-resolved) and sets it to 100.100.100.100, which then has
regular DNS via the metadata IP and *.internal DNS via the metadata IP
as well. If the tailnet configures explicit DNS servers, those are used
instead, except for *.internal.

This also adds a new util/cloudenv package based on version/distro
where the cloud type is only detected once. We'll likely expand it in
the future for other clouds, doing variants of this change for other
popular cloud environments.

Fixes #4911

RELNOTES=Google Cloud DNS improvements

Change-Id: I19f3c2075983669b2b2c0f29a548da8de373c7cf
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
2 years ago
..
dnsconfig_test.go ipn/ipnlocal, net/dns*, util/cloudenv: specialize DNS config on Google Cloud 2 years ago
local.go ipn/ipnlocal, net/dns*, util/cloudenv: specialize DNS config on Google Cloud 2 years ago
local_test.go Update a Taildrop error message (#4818) 2 years ago
loglines_test.go ipn/store: add common package for instantiating ipn.StateStores 2 years ago
peerapi.go cmd/tailscaled,ipn/ipnlocal,wgengine/...: pass dns.Manager into netstack 2 years ago
peerapi_h2c.go wasm: exclude code that's not used on iOS for Wasm too 2 years ago
peerapi_macios_ext.go net/tsdial: move macOS/iOS peerapi sockopt logic from LocalBackend 3 years ago
peerapi_test.go ipn/ipnlocal: add start of inter-user Taildrop 2 years ago
ssh.go tempfork: temporarily fork gliderlabs/ssh and x/crypto/ssh 2 years ago
ssh_stub.go ssh: make it build on darwin 2 years ago
ssh_test.go ipn/ipnlocal: generate tailscaled-owned SSH keys as needed 2 years ago
state_test.go control/controlclient, ipn/ipnlocal: remove Client.SetExpirySooner, fix race 2 years ago