We're attempting to configure Azure Redis cache, I'm confident the connection string is correct as the logs suggests it's been able to make a connection. However my knowledge of using Redis with Sitecore is rather low. It looks like the issue is related to failed to nominate and No masters detected. It feels like we're missing something very obvious here.
3400 14:41:33 INFO <obfuscated>.redis.cache.windows.net:6380,password=<obfuscated>,ssl=True,abortConnect=False
3400 14:41:33 INFO
3400 14:41:33 INFO Connecting <obfuscated>.redis.cache.windows.net:6380/Interactive...
3400 14:41:33 INFO BeginConnect: <obfuscated>.redis.cache.windows.net:6380
3400 14:41:33 INFO 1 unique nodes specified
3400 14:41:33 INFO Requesting tie-break from <obfuscated>.redis.cache.windows.net:6380 > __Booksleeve_TieBreak...
3400 14:41:33 INFO Allowing endpoints 00:00:05 to respond...
3400 14:41:33 INFO Awaiting task completion, IOCP: (Busy=1,Free=999,Min=2,Max=1000), WORKER: (Busy=4,Free=32763,Min=2,Max=32767)
908 14:41:33 INFO EndConnect: <obfuscated>.redis.cache.windows.net:6380
908 14:41:33 INFO Configuring SSL
1128 14:41:34 INFO All tasks completed cleanly, IOCP: (Busy=2,Free=998,Min=2,Max=1000), WORKER: (Busy=6,Free=32761,Min=2,Max=32767)
1128 14:41:34 INFO <obfuscated>.redis.cache.windows.net:6380 faulted: UnableToResolvePhysicalConnection on PING
908 14:41:34 INFO Connect complete: <obfuscated>.redis.cache.windows.net:6380
1128 14:41:34 INFO All tasks are already complete
1128 14:41:34 INFO <obfuscated>.redis.cache.windows.net:6380 failed to nominate (Faulted)
1128 14:41:34 INFO > UnableToResolvePhysicalConnection on GET
1128 14:41:34 INFO No masters detected
1128 14:41:34 INFO <obfuscated>.redis.cache.windows.net:6380: Standalone v2.0.0, master; keep-alive: 00:01:00; int: Connecting; sub: Connecting; not in use: DidNotRespond
1128 14:41:34 INFO <obfuscated>.redis.cache.windows.net:6380: int ops=0, qu=0, qs=0, qc=1, wr=0, sync=1, socks=2; sub ops=0, qu=0, qs=0, qc=0, wr=0, socks=2
1128 14:41:34 INFO Circular op-count snapshot; int: 0 (0.00 ops/s; spans 10s); sub: 0 (0.00 ops/s; spans 10s)
1128 14:41:34 INFO Sync timeouts: 0; fire and forget: 0; last heartbeat: -1s ago
1128 14:41:34 INFO resetting failing connections to retry...
1128 14:41:34 INFO retrying; attempts left: 2...
1128 14:41:34 INFO 1 unique nodes specified
1128 14:41:34 INFO Requesting tie-break from <obfuscated>.redis.cache.windows.net:6380 > __Booksleeve_TieBreak...
1128 14:41:34 INFO Allowing endpoints 00:00:05 to respond...
1128 14:41:34 INFO Awaiting task completion, IOCP: (Busy=0,Free=1000,Min=2,Max=1000), WORKER: (Busy=6,Free=32761,Min=2,Max=32767)
1128 14:41:34 INFO All tasks completed cleanly, IOCP: (Busy=0,Free=1000,Min=2,Max=1000), WORKER: (Busy=6,Free=32761,Min=2,Max=32767)
1128 14:41:34 INFO <obfuscated>.redis.cache.windows.net:6380 returned, but incorrectly
1128 14:41:34 INFO Awaiting task completion, IOCP: (Busy=0,Free=1000,Min=2,Max=1000), WORKER: (Busy=6,Free=32761,Min=2,Max=32767)
5252 14:41:34 INFO Not all tasks completed cleanly, IOCP: (Busy=2,Free=998,Min=2,Max=1000), WORKER: (Busy=5,Free=32762,Min=2,Max=32767)
5252 14:41:34 INFO <obfuscated>.redis.cache.windows.net:6380 failed to nominate (WaitingForActivation)
5252 14:41:34 INFO No masters detected
5252 14:41:34 INFO <obfuscated>.redis.cache.windows.net:6380: Standalone v2.0.0, master; keep-alive: 00:01:00; int: Connecting; sub: Connecting; not in use: DidNotRespond
5252 14:41:34 INFO <obfuscated>.redis.cache.windows.net:6380: int ops=0, qu=2, qs=0, qc=0, wr=0, sync=1, async=2, socks=3; sub ops=0, qu=0, qs=0, qc=0, wr=0, socks=3
5252 14:41:34 INFO Circular op-count snapshot; int: 0 (0.00 ops/s; spans 10s); sub: 0 (0.00 ops/s; spans 10s)
5252 14:41:34 INFO Sync timeouts: 0; fire and forget: 0; last heartbeat: -1s ago
5252 14:41:34 INFO resetting failing connections to retry...
5252 14:41:34 INFO retrying; attempts left: 1...
5252 14:41:34 INFO 1 unique nodes specified
5252 14:41:34 INFO Requesting tie-break from <obfuscated>.redis.cache.windows.net:6380 > __Booksleeve_TieBreak...
5252 14:41:34 INFO Allowing endpoints 00:00:05 to respond...
5252 14:41:34 INFO Awaiting task completion, IOCP: (Busy=1,Free=999,Min=2,Max=1000), WORKER: (Busy=6,Free=32761,Min=2,Max=32767)
5252 14:41:39 INFO Not all tasks completed cleanly, IOCP: (Busy=2,Free=998,Min=2,Max=1000), WORKER: (Busy=5,Free=32762,Min=2,Max=32767)
5252 14:41:39 INFO <obfuscated>.redis.cache.windows.net:6380 did not respond
5252 14:41:39 INFO Awaiting task completion, IOCP: (Busy=2,Free=998,Min=2,Max=1000), WORKER: (Busy=5,Free=32762,Min=2,Max=32767)
1128 14:41:39 INFO Not all tasks completed cleanly, IOCP: (Busy=2,Free=998,Min=2,Max=1000), WORKER: (Busy=5,Free=32762,Min=2,Max=32767)
1128 14:41:39 INFO <obfuscated>.redis.cache.windows.net:6380 failed to nominate (WaitingForActivation)
1128 14:41:39 INFO No masters detected
1128 14:41:39 INFO <obfuscated>.redis.cache.windows.net:6380: Standalone v2.0.0, master; keep-alive: 00:01:00; int: Connecting; sub: Connecting; not in use: DidNotRespond
1128 14:41:39 INFO <obfuscated>.redis.cache.windows.net:6380: int ops=0, qu=2, qs=0, qc=0, wr=0, sync=1, async=5, socks=4; sub ops=0, qu=0, qs=0, qc=0, wr=0, socks=4
1128 14:41:39 INFO Circular op-count snapshot; int: 0 (0.00 ops/s; spans 10s); sub: 0 (0.00 ops/s; spans 10s)
1128 14:41:39 INFO Sync timeouts: 0; fire and forget: 0; last heartbeat: -1s ago
This question is very similar to AWS Redis session provider exception- No connection is available to service this operation: EVAL, but in this instance we're using Azure which is running 3.2.7 and no way of selecting a different version.
EDIT: Adding connection string
<obfuscated>.redis.cache.windows.net:6380,abortConnect=false,ssl=true,password=<obfuscated>
EDIT 2: Adding Web.config settings I tried
<add name="redis"
type="Sitecore.SessionProvider.Redis.RedisSessionStateProvider, Sitecore.SessionProvider.Redis"
applicationName="private"
host="<obfuscated>.redis.cache.windows.net"
port="6380"
accessKey="<obfuscated>"
ssl="true"
pollingInterval="2"
compression="true"
/>
