Just checked in the logs, the region is not actually dead after the exception

Apr  9 18:56:51 swoobat regiond[1297846]: TypeError: sequence item 0: expected str instance, ConnectionLost found
Apr  9 18:56:51 swoobat regiond[1297846]: regiond: [info] 127.0.0.1 POST /MAAS/api/2.0/machines/ HTTP/1.1 --> 500 INTERNAL_SERVER_ERROR (referrer: -; agent: Python-httplib2/0.20.2 (gzip))
Apr  9 18:57:07 swoobat maas-log[1302692]: maas.interface: [info] eno1 (physical) on swoobat: New MAC, IP binding observed: 14:02:ec:3e:e1:78, 10.244.40.159
Apr  9 18:57:07 swoobat maas-log[1302692]: Apr  9 18:56:46 meinfoo maas.rpc.rackcontrollers: [info] Existing rack controller 'swoobat' running version 3.5.0~rc9-16269-g.8ccfdc1b0 has connected to region 'meinfoo'.
Apr  9 18:57:07 swoobat maas-log[1302692]: Apr  9 18:57:07 meinfoo maas.interface: [info] eno1 (physical) on meinfoo: New MAC, IP binding observed: 14:02:ec:3e:e1:78, 10.244.40.159
Apr  9 18:57:07 swoobat maas-log[1302692]: Apr  9 18:57:07 leafeon maas.interface: [info] eno1 (physical) on leafeon: New MAC, IP binding observed: 14:02:ec:3e:e1:78, 10.244.40.159
Apr  9 18:57:15 swoobat rackd[1304815]: Uninitialized: [info] ClusterClient connection established (HOST:IPv6Address(type='TCP', host='::ffff:192.168.33.23', port=34234, flowInfo=0, scopeID=0) PEER:IPv6Address(type='TCP', host='::ffff:192.168.33.22', port=5252, flowInfo=0, scopeID=0))
Apr  9 18:57:15 swoobat rackd[1304815]: Uninitialized: [info] ClusterClient connection established (HOST:IPv6Address(type='TCP', host='::ffff:192.168.33.23', port=34250, flowInfo=0, scopeID=0) PEER:IPv6Address(type='TCP', host='::ffff:192.168.33.22', port=5252, flowInfo=0, scopeID=0))
Apr  9 18:57:15 swoobat rackd[1304815]: provisioningserver.rpc.clusterservice: [info] Event-loop 'meinfoo:pid=2128395' authenticated.
Apr  9 18:57:16 swoobat rackd[1304815]: provisioningserver.rpc.clusterservice: [info] Event-loop 'meinfoo:pid=2128395' authenticated.
Apr  9 18:57:16 swoobat maas-log[1302692]: Apr  9 18:57:16 meinfoo maas.rpc.rackcontrollers: [info] Existing rack controller 'swoobat' running version 3.5.0~rc9-16269-g.8ccfdc1b0 has connected to region 'meinfoo'.
Apr  9 18:57:16 swoobat rackd[1304815]: provisioningserver.rpc.clusterservice: [info] Rack controller '6m8qr6' registered (via meinfoo:pid=2128395) with MAAS version 3.5.0~rc9-16269-g.8ccfdc1b0.
Apr  9 18:57:16 swoobat rackd[1304815]: provisioningserver.rpc.clusterservice: [info] Rack controller '6m8qr6' registered (via meinfoo:pid=2128395) with MAAS version 3.5.0~rc9-16269-g.8ccfdc1b0.
Apr  9 18:57:17 swoobat regiond[1297844]: twisted.internet.protocol.Factory: [info] RegionServer connection established (HOST:IPv6Address(type='TCP', host='::ffff:10.245.222.223', port=5251, flowInfo=0, scopeID=0) PEER:IPv6Address(type='TCP', host='::ffff:10.245.222.182', port=34344, flowInfo=0, scopeID=0))
Apr  9 18:57:17 swoobat regiond[1297844]: twisted.internet.protocol.Factory: [info] RegionServer connection established (HOST:IPv6Address(type='TCP', host='::ffff:10.245.222.223', port=5251, flowInfo=0, scopeID=0) PEER:IPv6Address(type='TCP', host='::ffff:10.245.222.182', port=34354, flowInfo=0, scopeID=0))
Apr  9 18:57:17 swoobat regiond[1297844]: maasserver.rpc.regionservice: [info] Rack controller authenticated from '::ffff:10.245.222.182:34344'.
Apr  9 18:57:17 swoobat regiond[1297844]: maasserver.rpc.regionservice: [info] Rack controller authenticated from '::ffff:10.245.222.182:34354'.


If the regiond was actually starting again there should be other log statements about twisted and other startup messages