[DishyDev]

As someone whose job involves maintaining uptime of a critical system that's dependent on Cosmos DB this sort of thing is scary. Where there's been other reliability issues with Cosmos before we've not had an understanding customer base, and it feels very out of my control.

I'm finding a lot of the reliability guarantees of Azure PaaS services are overblown or come with big caveats when you start to work with them in a serious way. For example I've had some bad reliability issues with Azure Functions not firing, or their premium function runtimes becoming unresponsive. And it seems like that's just the start of the outstanding issues with them https://github.com/Azure/azure-functions-host/issues

I think people need to look more carefully at these PaaS guarantees and look at what that 99.999% reliability Microsoft are claiming actually means.

[nijave]

After using AWS for 3+ years and GCP for about 6 months, I can say Azure significantly lags behind them. Their service reliability is astonishingly poor. I think our most recent issue was 67 VM failures in a VMSS (of 55 nodes) backing AKS (Azure Kubernetes Service) in a single month. The health events said there were some kind of "remote storage errors" making the VMs unhealthy

That's a couple months after the Ubuntu/systemd incident (Azure's "blessed" Linux image is Ubuntu and it has unatttended-upgrades enabled including on managed infrastructure like AKS (where you can't turn it off without dirty hacks). A bad Ubuntu update caused hosts to lose their DNS from DHCP config rendering massive amounts of machines in partially broken states)

https://thenewstack.io/ubuntu-linux-and-azure-dns-problem-gi...

[xiwenc]

Do you know what blew me off? When azure executes maintenance on for instance postgresql servers, there is no record of that activity in the activity logs or anything to note in service health. The service was unavailable during the maintenance. And stronger yet when the database is unusable due to an incident the cpu is maxed out and it doesnt allow any successful connection, nothing is detected.

How can this be a premium iaas/paas? Azure feels like the MS teams of tele conference. Companies buy in because they are already in the MS world. Not because azure is better.

[nijave]

Postgres on Azure is terrible. Were you using Single Server, Flexible or Hyperscale/Citus?

[xiwenc]

Single servers now. We are considering to move to flexible server or just database as a service (non-server)

[nijave]

Yeah, that's the one we've had a lot of problems with.

> And stronger yet when the database is unusable due to an incident the cpu is maxed out and it doesnt allow any successful connection, nothing is detected

Apparently Azure's storage system that backs this uses some sort of thread pool and the thread pool can lock up/become exhausted leading to I/O starvation. When this happens, connection attempts fail. When the connection attempts fail, it can lead to a connection storm where all these new connections rolling in exhaust the CPU. The telltale indicator is Postgres checkpoints getting behind.

All the while, the DB I/O metrics look like they're completely fine because it's not hitting an I/O limit, it's hitting thread pool exhaustion in the some storage system under the instance, outside of Postgres.

You can also get some clues if this is the problem by enabling Performance Insights and checking the Waits tab. If all the top waits are related to I/O activity, that's another dead giveaway the storage system is locked up again. You can just web search the name of the waits to see what causes them. AWS has some nice docs detailing Postgres waits

[xiwenc]

Thanks for the detailed explanation! We didnt look into this so detailed yet but what you are describing sounds familiar.

Since we have premium support (P1?), we had some internal azure postgresql engineer look at the issue and they pushed the problem back to us. Blaming our app not built correctly. That has been ping-ponging for over a year now.

Finally i saw this semi-acknowledgment in their health status yesterday.

Do you happen to know a proper solution? Are you waiting for them to fix this issue or moved to a different db service?

Perhaps the flexible server is better?

[nijave]

We've talked to the Postgres product engineers many times. Proper solution is to run away from Single Server as quick as possible. Flexible or Citus Hyperscale may be good solutions. We're currently using Patroni to manage VM-based clusters (but still have a lot of data on SS)

Personally, I'd look into a 3rd party if you want managed Postgres (assuming you don't have contractual obligations that might complicate 3rd party access). There's vendors like EnterpriseDB, Scalegrid, etc that provide various solutions (I don't have any recomendations here--Postgres has a list of managed providers by country https://www.postgresql.org/support/professional_hosting/nort...)

[xiwenc]

The gods are angry i think. Woke up today and all our pg servers were unavailable. Checked service health and azure shows a global pg incident impacting pg servers.

And the funny thing? Status.azure.com is all green. No events in activity overview. No service health within the affected instance.

Workaround advised by azure? Upgrade to next plan. We already reached the maximum size. Maybe time for Citus . More $$$ for M$

[djbusby]

Premium is a price point not a service level

[xiwenc]

Indeed. Typical case where the purchasing people are not the same people that has to use it day to day.

[aoetalks]

That feels broken. Did you open a support ticket or a GH issue on the documentation page?

[rrdharan]

Even as bad as their reliability issues are, I'd still be more worried about their security issues:

https://www.wiz.io/blog/chaosdb-explained-azures-cosmos-db-v... https://msrc-blog.microsoft.com/2021/08/27/update-on-vulnera...

[ethbr0]

> I think people need to look more carefully at these PaaS guarantees and look at what that 99.999% reliability Microsoft are claiming actually means.

Hypercloud managed service SLAs: all the fun of novel complex, technical solutions in production + the transparency of cast iron + the pendanticism of being a contract lawyer

Which leaves exactly zero people who are excited to be at that intersection.

[wharfjumper]

Asking as someone who knows nothing about CosmosDB other than the frequent negative comments I read on HN, do you know what led to you using it?