Why is my WebApp only allowed to make 128 connections to an Oracle Database

Matthew Norman 20

we have a (slotted) web app that makes connections (via hcm/relay) to an on prem Oracle database. we were asked to put a scheduled flush of the app service (a pipeline containing only a 'Stop Azure App Service' followed by a 'Start Azure App Service' task against the existing production slot only) which now runs weekly. However since the first run , app insights is reporting Oracle.ManagedDataAccess.Client.OracleException at OracleInternal.ConnectionPool.PoolManager errors once the relay is reporting 128 Active Connections. Prior to running this pipeline we were able to get to roughly 1500 connections before seeing any issues, but now it seems like a hard 128 limit. Nothing else has changed other than the stop/start pipeline being run.

brtrach-MSFT 16,676 Reputation points Microsoft Employee

2023-11-22T23:02:35.15+00:00

@Matthew Norman Please let us know if the below answer was helpful by accepting it as the answer. If you have further questions or concerns, reply to this message and we will assist you further.

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brtrach-MSFT 16,676 Reputation points Microsoft Employee

2023-11-16T02:38:17.7633333+00:00

@Matthew Norman This does not initially appear to be a limitation of the Azure App Service platform, which I am most knowledgeable to speak on. My belief for this reasoning is that the number of connections allowed is normally in the 1,000s depending on the size of your instance.

This is likely a limitation within Oracle that you are hitting. From my research, Oracle seems to impose a limit of around 100 connections. You can increase the limit as described here: https://docs.oracle.com/en/database/oracle/oracle-database/21/jjucp/controlling-pool-size.html#GUID-1909EBD1-E526-4385-9A2A-39C89F985A14

How high you set the limit is ultimately up to you and the strength of your Oracle server. It's also recommended that you ensure your code is optimized to close connections when it is finished with them.

Again, please keep in mind that I am not an Oracle specialist, but I hope this helps get you pointed the right direction. Reply back to this answer if I can assist you further.
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Matthew Norman 20 Reputation points

2023-11-16T08:20:58.68+00:00

Thanks for this. We already have the connection string to Oracle and the max connections on the oracle server set to 400, so I'd expect it to fall over there. I did see an article about SNAT ports only having 128 connections (https://learn.microsoft.com/en-us/azure/app-service/troubleshoot-intermittent-outbound-connection-errors) so was wondering if that might be connected.

But also we have only seen this behaviour (a reduction in the allowed connections from 1500ish to a hard 128) after we started running the pipeline below - but this is a slotted set up the staged slot might have an impact so was wondering if the fact we don't stop the staging slot web app is causing an issue

stages: - stage: RestartOfWebApp jobs: - job: StopWebApp steps: # Stop the app service - task: AzureAppServiceManage@0 displayName: 'Stop WebApp' inputs: action: 'Stop Azure App Service' azureSubscription: ${{ variables.serviceConnection }} resourceGroupName: ${{ variables.azureResourceGroup }} webAppName: ${{ variables.appServiceName }} - job: StartWebApp dependsOn: StopWebApp steps: # Stop the app service - task: AzureAppServiceManage@0 displayName: 'Start WebApp' inputs: action: 'Start Azure App Service' azureSubscription: ${{ variables.serviceConnection }} resourceGroupName: ${{ variables.azureResourceGroup }} webAppName: ${{ variables.appServiceName }}

brtrach-MSFT 16,676 Reputation points Microsoft Employee

2023-11-21T02:35:28.5066667+00:00

My apologies for the delay, I was out for a few days.

After looking at this with a fresh set of eyes, you might be right that you are hitting the app service 128 snat port limit. The best way to confirm this though would be to verify using 'diagnose and solve problems' blade within your web app. This is a powerful tool and is using the same data that our support engineers use. Once inside the blade, click on 'availability and performance' and then find the report called 'SNAT Port Exhaustion'. See if anything appears in the report. Be careful to ensure the time range is wide enough to include the period of time where you encountered the issue/error (time is in UTC).

When SNAT port exhaustion occurs, we suggest to customers a list of suggestions:

Update your project code to reuse and close out connections.

Use connection pooling when possible.

Use an App Gateway as it raises your limit to 64,000 connections.

App Gateway would be the quickest way to band-aid your web app to ensure the failures stop happening. It would then give your developers ultimately more time to ensure steps 1 and 2 are implemented as possible.
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Why is my WebApp only allowed to make 128 connections to an Oracle Database

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