What has happened with Azure managed Redis instances yesterday at 18:04 UTC?

Question

What has happened with Azure managed Redis instances yesterday at 18:04 UTC?

Maksim Pariy 0

Hello

Our Azure Managed Redis instance suddenly became unavailable for a few minutes, so we lost connection to it, and our application sent many 504 responses to our clients.

It seems that both backend instances were rebooted simultaneously.

redis_screen.png

Please explain what happened at this time to avoid such situation in the future

Best regards

Maksim

Mahesh Kurva 5,025 Reputation points Microsoft External Staff Moderator

2025-05-08T18:04:40.11+00:00

Hi Maksim Pariy,

I kindly request you to provide the details mentioned in the private message so we can identify the root cause and address the issue effectively.
Mahesh Kurva 5,025 Reputation points Microsoft External Staff Moderator

2025-05-09T16:48:53.8766667+00:00

Hi Maksim Pariy,

We received an update from our internal team indicating that everything was functioning correctly and the cache was fine on 05/08 at 18:04 UTC.

Could you please confirm if this timeframe is accurate?
Mahesh Kurva 5,025 Reputation points Microsoft External Staff Moderator

2025-05-09T20:08:44.7766667+00:00

Hi Maksim Pariy,

Thanks for sharing the information.

We are reaching out to the internal team to get more information related to your query and will get back to you as soon as we have an update.
Mahesh Kurva 5,025 Reputation points Microsoft External Staff Moderator

2025-05-14T00:45:07.24+00:00

Hi Maksim Pariy,

If my response addressed your query, hope this helps. Do let us know if you any further queries.

If this answers your query, do click Accept Answer and Yes for was this answer helpful. And, if you have any further query do let us know.
Maksim Pariy 0 Reputation points

2025-05-14T06:54:53.3466667+00:00

hi, you didn't answer my questions in comment to your public answer, so I wouldn't accept this.
Maksim Pariy 0 Reputation points

2025-05-14T06:58:08.9066667+00:00

We want to be sure it doesn't happen again in the future. If not, we will be forced to stop using this service because it is unstable
Mahesh Kurva 5,025 Reputation points Microsoft External Staff Moderator

2025-05-26T17:31:22.8466667+00:00

Hi Maksim Pariy,

Just checking in to see if my response addressed your query, hope this helps.

If this answers your query, do click Accept Answer and Yes for was this answer helpful. And, if you have any further query do let us know.

1 answer

Your answer

Mahesh Kurva 5,025 Reputation points Microsoft External Staff Moderator

2025-05-08T18:04:40.11+00:00

Hi Maksim Pariy,

I kindly request you to provide the details mentioned in the private message so we can identify the root cause and address the issue effectively.
Mahesh Kurva 5,025 Reputation points Microsoft External Staff Moderator

2025-05-09T16:48:53.8766667+00:00

Hi Maksim Pariy,

We received an update from our internal team indicating that everything was functioning correctly and the cache was fine on 05/08 at 18:04 UTC.

Could you please confirm if this timeframe is accurate?
Mahesh Kurva 5,025 Reputation points Microsoft External Staff Moderator

2025-05-09T20:08:44.7766667+00:00

Hi Maksim Pariy,

Thanks for sharing the information.

We are reaching out to the internal team to get more information related to your query and will get back to you as soon as we have an update.
Mahesh Kurva 5,025 Reputation points Microsoft External Staff Moderator

2025-05-14T00:45:07.24+00:00

Hi Maksim Pariy,

If my response addressed your query, hope this helps. Do let us know if you any further queries.

If this answers your query, do click Accept Answer and Yes for was this answer helpful. And, if you have any further query do let us know.
Maksim Pariy 0 Reputation points

2025-05-14T06:54:53.3466667+00:00

hi, you didn't answer my questions in comment to your public answer, so I wouldn't accept this.
Maksim Pariy 0 Reputation points

2025-05-14T06:58:08.9066667+00:00

We want to be sure it doesn't happen again in the future. If not, we will be forced to stop using this service because it is unstable
Mahesh Kurva 5,025 Reputation points Microsoft External Staff Moderator

2025-05-26T17:31:22.8466667+00:00

Hi Maksim Pariy,

Just checking in to see if my response addressed your query, hope this helps.

If this answers your query, do click Accept Answer and Yes for was this answer helpful. And, if you have any further query do let us know.

Answer 1

Mahesh Kurva 5,025 Microsoft External Staff Moderator

Hi Maksim Pariy,

The problem happened on 05/07 between 18-00 and 18-05 UTC

On May 7, 2025, at 17:57 UTC, performed scheduled maintenance on the "symfony" cache as part of our regular software update process. During these events, infrastructural changes were made to the cache. These changes are neither reboots nor simultaneous, but they might cause brief connectivity interruptions. These temporary disruptions are expected as part of the upgrade process. Please check the following document to understand the patching process.

Document: https://learn.microsoft.com/en-us/azure/redis/failover#how-does-patching-occur

We understand how important uninterrupted service is to you, and we sincerely apologize for any inconvenience this may have caused. These updates are essential to ensure continued performance, security, and reliability of our systems.

Recommendation**:**

We suggest follow the best practices given for connection resiliency to prevent connectivity issues during maintenance events: Best practices for connection resilience for Azure Managed Redis(preview) - Azure Managed Redis | Microsoft Learn.

Hope this helps. Do let us know if you any further queries.

If this answers your query, do click Accept Answer and Yes for was this answer helpful. And, if you have any further query do let us know.

Maksim Pariy 0 Reputation points

2025-05-13T17:14:39.1033333+00:00

Hi,

Thanks for the information.

But how is it possible that both replicas of this instance were rebooted at the same time and caused the service to fail? This instance has high availability and data replication, so it should not cause disruptions. But it doesn't work as it should.

Also, after this patch, it looks like the Redis cache instance is not working properly. Our PHP slow log shows that there are some delays and interruptions in data processing. After we migrated to a new instance with the same parameters, this problem has gone away
Mahesh Kurva 5,025 Reputation points Microsoft External Staff Moderator

2025-05-23T22:40:03.5966667+00:00

Hi Maksim Pariy,

During scheduled maintenance on Azure Cache for Redis, infrastructural changes can cause brief connectivity interruptions. These changes are expected as part of the upgrade process and are not simultaneous reboots.

Regarding failover/patching, this should help Failover and patching - Azure Cache for Redis | Microsoft Learn

Reboot, Flush, and Schedule Updates Azure Cache for Redis - Azure Cache for Redis | Microsoft Learn

We recommend that you follow Azure's best practices for connection resilience with Managed Redis. This should help ensure that you don't encounter the same issue in the future.

I hope this information helps. Please do let us know if you have any further queries.
Mahesh Kurva 5,025 Reputation points Microsoft External Staff Moderator

2025-05-27T19:36:38.75+00:00

Hi Maksim Pariy,

Following up to see if the above answer was helpful. If this answers your query, do click Accept Answer and Yes for was this answer helpful. And, if you have any further query do let us know.

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What has happened with Azure managed Redis instances yesterday at 18:04 UTC?

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