server: code cleanup and documentation #39452
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the `netutil.Server` is really a multi-purpose thing. This patch extends the comment to explain what it does in more details. Release note: None
This patch performs the following cleanups and refactors: - adds explanatory comments; - factors the call to net.Listen and starting the server for the admin UI into a new method `(*Server).startServeUI()`. - factors the call to net.Listen and starting the RPC server into a new method `(*Server).startServeRPC()`. - factors the start of the SQL server into a new method `(*Server).startServeSQL()`. - extracts the TCP keepalive configuration function into a top-level function (was a closure). Release note: None
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39305: server,config,cli: offer a separate port for SQL clients r=knz a=knz (First two commits from #39452) Fixes #30828. Fixes #5816. his patch introduces the ability to split off the SQL server into a separate port, using the new command-line flag `--sql-addr`. The remainder of this commit message details: - the motivation for the change - some usage documentation for users of the new feature - how to introduce this feature in existing clusters - reading recommendations to reviewers of this change - release note **Motivation** This is a long- and oft-requested feature, aimed at facilitating deployments in professional networks that use firewalls to fence off "internal" (server-side) traffic from external (client) traffic. **Usage** How it works (simplified): - the flag `--sql-addr` indicates on which host/port to listen to for SQL connections. - it is possible to specify `--sql-addr` to be equal to `--listen-addr`, in which case both will share a single TCP connection (internally: using `cmux`). - in fact, the default for `--sql-addr` is to be equal to `--listen-addr`, for compatibility with previous versions of CockroachDB. - when `--sql-addr` and `--listen-addr` are different, then the server does not accept SQL connections any more on the `--listen-addr` address. - the flag `--advertise-sql-addr` complements `--sql-addr` in the same way as `--advertise-addr` complements `--listen-addr`. In addition, the output of `cockroach node status` (and the contents of `crdb_internal.gossip_nodes`) is extended to display the SQL address. Note (intermediate): the new flags enables both using separate ports on the same host address (e.g. listening on 127.0.0.1 with separate ports for SQL and RPC), and also using the same port on separate host addresses (e.g. listening on 127.0.0.1:26257 for SQL, and 192.168.2.123:26257 for RPC). Both use cases are legitimate and have seen demand in the wild. Note (advanced): the computation of defaults is performed separately for the host and port part of the flag. The logic is the same as that used for `--http-addr`, using default port 26257. For example, `--sql-addr=localhost` (without port number) is equivalent to `--sql-addr=localhost:26257`. Note (advanced): the computation of defaults for `--advertise-sql-addr` is a bit non-trivial as it pulls its address and port part separately from `--sql-addr`, `--listen-addr` and `--advertise-addr`. Effort was made to ensure sane defaults when some flags but not all are omitted. This is best explained by examples, see the unit tests in flags_test.go for details. **Upgrading a cluster to use separate ports** If a cluster is already online and the need arises to split the ports, the flag can be introduced as follows: - when keeping port 26257 for SQL: 1. restart all nodes in a rolling fashion, updating the `--join` flag on each node to add the new RPC address. 2. restart all nodes in a rolling fashion, adding `--sql-addr=:26257` and setting `--listen-addr=xxx` to the new RPC address. The previous address with port 26257 can also be removed from `--join` in the same step. - when keeping port 26257 for RPC, introducing a new SQL addr/port: 1. if load balancers are in use, extend the load balancer config to also attempt connections on the new SQL address. If load balancers are not in use, temporarily add one that accepts clients on the old addr/port and redirects the connection on both the new addr/port and the old. 2. restart all nodes in a rolling fashion, updating the `--sql-addr` flag. **Review notes** This change was constructed as follows: 1. introducing new fields in `base.Config` 2. implementing the address validation logic in `addr_validation.go` and corresponding unit tests. 3. picking up the new fields to listen separately in `(s *Server) startListenRPCAndSQL()` 4. adding the command line flag parsing and default logic in `flags.go` and corresponding unit tests. 5. manually testing that indeed the server can listen separately on separate ports. 6. to ensure that most unit tests also exercise the split ports, make TestServer/TestCluster set the new flags `SplitListenSQL` 7. extend the TestServer interface to make the SQL address available alongside the RPC address. 8. update all the tests using a SQL connection to use the SQL address 9. update the CLI test logic from `cli_test.go` to configure the `--host` flag to the RPC or SQL address depending on the command being invoked. At this point all tests except for `TestZip` would pass successfully. The remainder of the work is for the benefit of `cockroach zip`, which needs to discover the reachable address of every node in a cluster from the address of just 1 of them, doing so by inspecting all the node descriptors. `cockroach zip` is also peculiar in that it uses both the RPC and SQL interfaces. 1. equip the node descriptor with a field for the SQL address and ensure it gets populated. 2. make the zip logic fetch the SQL address of the primary node by a Node() status request over RPC. 3. for the loop over all nodes, use the SQL address in each node's descriptor for SQL queries separately from the RPC logic. Release note (cli change): CockroachDB now recognizes a flag `--sql-addr` which makes it possible to accept connections by clients on a separate TCP address and/or port number from the one used for intra-cluster (node-node) connections. This is aimed to enable firewalling client traffic from server traffic. Co-authored-by: Raphael 'kena' Poss <knz@cockroachlabs.com>
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(Pulled out of #39305 to ease review)