Nick Gotch's questions

I'm running an OpsWorks stack with:

• 10 c3.2xlarge instances running across 4 availability zones.
• The CPU never surpasses 5% on each instance.
• Each instance is connecting (through a memcached layer) to a db.r3.8xlarge (32 vCPU, 244 GiB RAM) RDS instance.
• The DB's CPU is staying nicely between 15-20 percent.
• Each EC2 instance is set to 250 connections with the RDS (total 2,500 connections).
• Each instance's memory is gradually increasing but I think this is a separate issue.
• The load_1, load_5, load_10 metrics are all really high 0.9-1.0.
• The active concurrent users connecting (based on a 3 minute window) are getting stuck at between 2500-3000 connections.

We tried increasing RDS instance size and while it did stop our RDS from maxing out we're trying to figure out why the conncurrent connections seems to be pegging.

Is there some setting in the ELB that limits connections? The latency for calls is really high. I'm just trying to figure out something which might be throttling this since all the hardware seems to be running okay.

I have a Windows 7 host machine running Fiddler and a Ubuntu VirtualBox guest. On the host I'm running a client app (native, not .NET or Java) that allows me to set the server name and port but there are no proxy setting options. It's connecting to a REST server running in the Ubuntu guest.

It works fine making calls into and out of the guest but I haven't been able to get Fiddler to log the traffic. I tried setting up a Rule (though I'm not sure I did it correctly) and tried instructions for using Fiddler as a reverse proxy and setting up an outgoing port on the Ubuntu machine without success.

If I point the client to 127.0.0.1 and port 8888 I can see the first request but that's about it (and the client obviously doesn't work configured like this).

Does someone know what steps I can take to get Fiddler logging the traffic?

I'm a developer but I have a question that seems belongs more in the ServerFault category than StackOverflow.

We have a production service that every so often tends to throw:

System.Runtime.InteropServices.COMException: Call was canceled by the message filter. (Exception from HRESULT: 0x80010002 (RPC_E_CALL_CANCELED))

The code that's triggering this error is using WMI to get network interface MAC addresses. I have replacement code that doesn't use WMI but we need to verify the issue before/after the change. My question then is: How can I artificially recreate the error message generated above?