modules/patroni/default.nix

@@ -183,6 +183,13 @@ in
       };
       description = mdDoc "Environment variables made available to Patroni as files content, useful for providing secrets from files.";
     };
+
+    migrations = {
+      enable = mkEnableOption "automatic migrations";
+
+      
+      
+    };
   };
 
   config = mkIf cfg.enable {
@@ -192,6 +199,10 @@ in
       inherit (cfg) name;
       inherit (cfg) namespace;
 
+      bootstrap = mkIf cfg.migrations.enable {
+        dcs.postgresql.parameters.wal_level = "logical";
+      };
+
       restapi = {
         listen = "${cfg.nodeIp}:${toString cfg.restApiPort}";
         connect_address = "${cfg.nodeIp}:${toString cfg.restApiPort}";
@@ -238,6 +249,187 @@ in
         wantedBy = [ "multi-user.target" ];
         after = [ "network.target" ];
 
+        preStart = let
+          upgradeScript = pkgs.writers.writePython3 "patroni-migration-self-upgrade" {
+            libraries = [ (pkgs.python3Packages.toPythonModule patroni) ];
+            flakeIgnore = [
+              "E501"
+            ];
+          } ''
+            import os
+            import subprocess
+            from datetime import datetime
+            from patroni.__main__ import Patroni
+            from patroni.config import Config
+            from patroni.utils import polling_loop
+            
+            if __name__ == "__main__":
+                print("creating patroni control object")
+                ctl = Patroni(Config(os.getenv("PATRONICTL_CONFIG_FILE")))
+                pg = ctl.postgresql
+
+                print("running initdb")
+                pg.bootstrap._initdb(ctl.config.get("initdb"))
+
+                configuration = pg.config.effective_configuration
+
+                print("configuring postgres")
+                pg.config.check_directories()
+                pg.config.write_postgresql_conf(configuration)
+                pg.config.resolve_connection_addresses()
+                pg.config.replace_pg_hba()
+                pg.config.replace_pg_ident()
+
+                print("starting postgres")
+                pg.start()
+
+                auth = pg.config.get("authentication")
+                listen = pg.config.get("listen").split(":")
+                leader_host = os.getenv("PATRONIMIGRATOR_LEADER_HOST")
+                leader_port = os.getenv("PATRONIMIGRATOR_LEADER_PORT")
+
+                def psql(host=listen[0], port=listen[1], user=auth["superuser"]["username"]):
+                    return lambda query: subprocess.run([
+                        pg.pgcommand("psql"),
+                        "-h", host,
+                        "-p", port,
+                        "-U", user,
+                        "-f", "-"
+                    ], input=(query if type(query) is bytes else query.encode("utf8")))
+
+                print("dumping schema")
+                args = [
+                    pg.pgcommand("pg_dumpall"),
+                    "-h", leader_host,
+                    "-p", leader_port,
+                    "-U", auth["superuser"]["username"],
+                    "-s"
+                ]
+                print("running with args:")
+                print(args)
+                dump = subprocess.run(args, capture_output=True)
+            
+                psql_self = psql()
+                psql_leader = psql(
+                    host=leader_host,
+                    port=leader_port
+                )
+                print("applying schema")
+                psql_self(dump.stdout)
+                ctime = int((datetime.utcnow() - datetime(1970, 1, 1)).total_seconds())
+                pub = f"pub_live_upgrade_{ctime}"
+                sub = f"sub_live_upgrade_{ctime}"
+                replication_user = auth["superuser"]["username"]
+                all_databases = pg.query("SELECT datname FROM pg_database WHERE datistemplate = false;").fetchall()
+                for (db,) in all_databases:
+                    print(f"creating pub/sub for database {db}")
+                    psql_leader(f"""
+                    \\connect {db}
+                    CREATE PUBLICATION {pub}_{db} FOR ALL TABLES;
+                    """)
+                    psql_self(f"""
+                    \\connect {db}
+                    CREATE SUBSCRIPTION {sub}_{db} CONNECTION 'host={leader_host} port={leader_port} dbname={db} user={replication_user}' PUBLICATION {pub}_{db};
+                    """)
+
+                # TODO: should probably wait longer
+                for _ in polling_loop(300):
+                    print("waiting for synchronization to complete")
+                    laststate = "?"
+                    for (state,) in pg.query("""
+                            SELECT srsubstate FROM pg_subscription_rel;
+                            """):
+                        laststate = state
+                        if state != "r":
+                            print(f"sync state={state}")
+                            break
+                    if laststate == "r":
+                        break
+                print("synchronized!")
+                for (db,) in all_databases:
+                    print(f"dropping pub/sub for database {db}")
+                    psql_self(f"""
+                    \\connect {db}
+                    DROP SUBSCRIPTION {sub}_{db};
+                    """)
+                    psql_leader(f"""
+                    \\connect {db}
+                    DROP PUBLICATION {pub}_{db};
+                    """)
+
+                [(sysid,)] = pg.query("SELECT system_identifier FROM pg_control_system();").fetchall()
+                print(f"setting system identifier to {sysid}")
+                ctl.dcs.initialize(create_new=False, sysid=str(sysid))
+                pg.stop()
+          '';
+          migrationScript = pkgs.writeShellScript "patroni-migration-replicate-or-self-upgrade" ''
+            if [[ "$(consul catalog nodes --service='${cfg.scope}' 2>/dev/null | wc -l)" -gt 0 ]]; then
+              # check if there's an active leader
+              leader="$(patronictl list -f json | jq -r 'map(select(.Role == "Leader" and .State == "running") | .Member) | .[0]')"
+              if [[ -n "$leader" ]]; then
+                leaderVersion="$(patronictl version '${cfg.scope}' "$leader" | grep -o 'PostgreSQL [0-9]*' | cut -d' ' -f2)"
+                if [[ "$leaderVersion" == '${postgresql.psqlSchema}' ]]; then
+                  # leader is the same version as our target
+                  echo leader is at target version, preparing for reinit
+                  # TODO: need to wipe data dir, or will patroni do it for us?
+                  rm -rf '${cfg.postgresqlDataDir}'
+                  exit 0
+                else
+                  echo leader version $leaderVersion differs from target version ${postgresql.psqlSchema}, trying to find an upgraded replica
+                  for replica in $(patronictl list -f json | jq -r 'map(select(.Role == "Replica" and .State == "running") | .Member) | .[]'); do
+                    replicaVersion="$(patronictl version '${cfg.scope}' "$replica" | grep -o 'PostgreSQL [0-9]*' | cut -d' ' -f2)"
+                    if [[ "$replicaVersion" == '${postgresql.psqlSchema}' ]]; then
+                      # another replica is the same version as us, make leader
+                      echo found a replica with the same target version, attempting to promote it to leader
+                      # TODO: do we need to force it to become the leader or is there another way?
+                      if ! patronictl switchover '${cfg.scope}' --master "$leader" --candidate "$replica" --force --scheduled now; then
+                        echo switchover failed! attempting failover
+                        patronictl failover '${cfg.scope}' --candidate "$replica" --force
+                      fi
+                      while [[ "$(patronictl list -f json | jq -r 'map(select(.Role == "Leader" and .State == "running") | .Member) | .[0]')" != "$replica" ]]; do
+                        echo waiting for "$replica" to become the leader
+                        patronictl list
+                        sleep 1
+                      done
+                      echo preparing for reinit after leader promotion
+                      # TODO: need to wipe data dir, or will patroni do it for us?
+                      rm -rf '${cfg.postgresqlDataDir}'
+                      exit 0
+                    fi
+                  done
+                  echo no other nodes are at the target version, performing self-upgrade
+                  leaderHost="$(patronictl list -f json | jq -r 'map(select(.Role == "Leader" and .State == "running") | .Host) | .[0]')"
+                  # this is where it gets spicy
+                  rm -rf '${cfg.postgresqlDataDir}'
+                  install -dm700 '${cfg.postgresqlDataDir}'
+                  # give the migration script 1800 seconds
+                  systemd-notify EXTEND_TIMEOUT_USEC=1800000000
+                  export PATRONIMIGRATOR_LEADER_HOST="$leaderHost"
+                  # HACK: find a way to get the port
+                  export PATRONIMIGRATOR_LEADER_PORT="5432"
+                  exec ${upgradeScript}
+                fi
+              fi
+            fi
+            echo consul returned no nodes, proceeding with cluster bootstrap
+            # no other nodes around, nothing we can do
+          '';
+        in mkIf cfg.migrations.enable /*bash*/ ''
+          export PATH=${makeBinPath [ pkgs.jq pkgs.gnugrep config.services.consul.package patroni ]}:$PATH
+          export PATRONICTL_CONFIG_FILE=${configFile}
+          set -e
+          pgVersion='${cfg.postgresqlDataDir}/PG_VERSION'
+          # don't do anything if already at the target version
+          if [[ -e "$pgVersion" && "$(<"$pgVersion")" == '${postgresql.psqlSchema}' ]]; then
+            echo data directory version is target, no migrations to run
+            exit 0
+          fi
+          # HACK:
+          export CONSUL_HTTP_ADDR=192.168.1.4:8500
+          # ask consul if there are any other nodes around
+          exec consul lock --verbose --child-exit-code --shell=false '/patroni-migrator-upgrade/${cfg.scope}' ${migrationScript}
+        '';
+
         script = ''
           ${concatStringsSep "\n" (attrValues (mapAttrs (name: path: "export ${name}=\"$(<'${path}')\"") cfg.environmentFiles))}
           exec ${patroni}/bin/patroni ${configFile}
@@ -288,10 +480,10 @@ in
             StateDirectoryMode = "0750";
           })
           (mkIf cfg.softwareWatchdog {
-            ExecStartPre = "+" + pkgs.writeShellScript "configure-software-watchdog.sh" ''
+            ExecStartPre = [("+" + pkgs.writeShellScript "configure-software-watchdog.sh" ''
               ${pkgs.kmod}/bin/modprobe softdog
               ${pkgs.coreutils}/bin/chown ${cfg.user} /dev/watchdog
-            '';
+            '')];
           })];
       };
     };
@@ -300,6 +492,7 @@ in
       patroni
       postgresql
       (mkIf cfg.raft pkgs.python310Packages.pysyncobj)
+      (pkgs.python3.withPackages (_: [ (pkgs.python3Packages.toPythonModule patroni) ]))
     ];
 
     environment.sessionVariables = {