SysAdmin

Loose Coupling and Discovery of Services With Consul — Part 1

Today I would like to demonstrate the use of Consul to help achieve loose coupling and discovery of services, two important principles of service-oriented architecture (SOA) present in modern, elastic infrastructures. If you have ever designed an architecture to be deployed in a cloud computing environment, then you are probably already familiar with the idea…

Comparing CPU Throughput of Azure and AWS EC2

After observing CPU core sharing with Amazon Web Services EC2, I thought it would be interesting to see if Microsoft Azure platform exhibits the same behavior. Signing up for Azure’s 30-day trial gives $200 in credit to use over the next 30-day period: more than enough for this kind of testing. Creating a new virtual…

SaltStack for Remote Parallel Execution of Commands

There are many scenarios when a SysAdmin has to do a “box walk” of the entire infrastructure to execute a command across many servers. This is universally accepted as one of the less glamorous parts of our job. The larger the infrastructure, the longer these box walks take, and the greater chance that human error…

vCPU sharing in EC2: HVM to the rescue?

aws-cpu-hvm-600x235

I’ve been doing some testing to clarify what a vCPU in Amazon Web Services actually is. Over the course of the testing, I experienced inconsistent results on a 2-thread test on a 4-vCPU m3.xlarge system, due to the mislabeling of the vCPUs as independent single-core processors by the Linux kernel. This issue manifests itself in…

Why was SSHD refusing my key?

I was contacted by a colleague about a problem he was having. “I’m trying to set up something simple which I’ve done millions of times, but it’s not working. I might be missing something obvious.” The issue was that the SSH public key authentication didn’t work. The environment was running a virtualized Oracle Enterprise Linux 6.4…

Troubleshooting ORA-27090 Async I/O Errors with Systemtap

There’s a known bug, 7306820 “ORA-7445 [krhahw] / ORA-27090 during file header read. Instances may crash, but this bug is fixed in 11.2.0.1, and this database is running 11.2.0.3. And on top of that, it’s an Exadata system, so I/O to storage servers goes over the InfiniBand network rather than using async I/O (AIO) calls.

Page 1 of 1012345...10...Last Page »