- Add function `validateServerAddress()` to `bdns/servers.go` which ensures that
DNS server addresses are TCP/ UDP dial-able per: https://golang.org/src/net/dial.go?#L281
- Add unit test for `validateServerAddress()` in `bdns/servers_test.go`
- Update `cmd/boulder-va/main.go` to handle `bdns.NewStaticProvider()`
potentially returning an error.
- Update unit tests in `bdns/dns_test.go`:
- Handle `bdns.NewStaticProvider()` potentially returning an error
- Add an IPv6 address to `TestRotateServerOnErr`
- Ensure DNS server addresses are validated by `validateServerAddress` whenever:
- `dynamicProvider.update() is called`
- `staticProvider` is constructed
- Construct server addresses using `net.JoinHostPost()` when
`dynamicProvider.Addrs()` is called
Fixes#5463
Abstract out the way that the bdns library keeps track of the
resolvers it uses to do DNS lookups. Create one implementation,
the `StaticProvider`, which behaves exactly the same as the old
mechanism (providing whatever names or addresses were given
in the config). Create another implementation, `DynamicProvider`,
which re-resolves the provided name on a regular basis.
The dynamic provider consumes a single name, does a lookup
on that name for any SRV records suggesting that it is running a
DNS service, and then looks up A records to get the address of
all the names returned by the SRV query. It exports its successes
and failures as a prometheus metric.
Finally, update the tests and config-next configs to work with
this new mechanism. Give sd-test-srv the capability to respond
to SRV queries, and put the names it provides into docker's
default DNS resolver.
Fixes#5306
Samantha
Aaron Gable