Category Archive: gotchas

Apr 07

Cloudera Manager Disaster Recovery with JSON Deployment Dump


Cloudera Manager is fairly opinionated. In its defence, it pretty much needs to be given that it needs to wrangle multiple underlying Open Source projects. Each of these, in turn, have their own quirks and opinions. The following is a description of how to recover a Cloudera Manager cluster post disaster, assuming that you have …

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Mar 30

Interesting Feature of Dockerfile Volume Directives

I’ve been rewriting a cleanroom version of the hadoop-in-a-box — just about finished. And, truth be told, the code, all in all, is a bit tighter than the original encumbered version. However, I ran into an interesting feature of Volumes — I had thought perhaps to optimize things a bit, but it caused some unexpected …

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Mar 17

Docker, Cgroups, Memory Constraints, and Java: A Cautionary Tale, or Here be Reapers (sometimes)


TL;DR: Java and cgroups/Docker memory constraints don’t always behave as you might expect. Always explicitly specify JVM heap sizes. Also be aware that kernel features may not be enabled. And Linux… lies. I’ve recently discovered an interesting “quirk” in potential interactions between Java, cgroups, Docker, and the kernel which can cause some surprising results. Unless …

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Mar 15

Zombie Apocalypse! Docker AUFS + Java + Low Memory …. Hadoop in a Box Cloudera Manager Cluster

TL;DR — When using AUFS in a memory constrained environment, Java can spawn (lots!) of Zombies. A workaround is to change the storage driver to the device mapper. In working on the Hadoop in a box CDH cluster with Cloudera Manager, I’ve discovered a few interesting things about AUFS. These experiences are with Ubuntu 14.04 …

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Mar 10

Cloudera Manager GUI and API Can Step on Each Other

While learning how the configuration worked — in particular which arguments to pass in order to set non-default values, I discovered that I could lose changes by following these steps: Use the GUI to set a value and save it. This is just so that you can find the variable. Keep the GUI open. Dump …

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Feb 11

Docker: Could not find container for entity id

I had an instance where the docker filesystem ran out of space. After cleaning up with docker rm and docker rmi, I got:

I followed iwidanalage‘s suggestion from “Creating fail with Could not find container for entity id after upgrading to 1.9.0 · Issue #17691 · docker/docker”

After this, it worked.

Sep 21

F5 LTM Monitoring and Wildfly

TL;DR The F5 BigPipe LTM uses HTTP/0.9 to send its HTTP monitoring requests by default. Wildfly 9.0 does not like this; moving to a monitor request of HTTP/1.1 fixed the problem. Caution: LTM 10.2.x and 11.x do not append a CR/LF to the end unless you are using Basic Authentication. This is contrary to previous …

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Sep 18

OBS for Videos

I recently discovered a really interesting tool for producing videos of screen captures, optionally with webcam inserts. It’s called Open Broadcaster Software and it works on Linux, Windows, and there is a beta version for Apple OSX. It seems that it was originally intended for streaming to websites, but it has a lot more features …

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Sep 07

Troubleshooting MicroSD Card Problems

The Computer employs Troubleshooters, whose job is to go out, find trouble, and shoot it. — Paranoia While re-imaging the MicroSD cards for my cluster, I ran into a few issues — nothing insurmountable, but I figured that I would share them to help others….. MicroSD cards generally come with an adapter to allow them …

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Apr 19

Docker Containers: Smaller is not always better

Generally smaller Docker containers are preferred to larger ones. However, a smaller container is not always as performant as a larger one. By using a (slightly) larger container, performance improved over 30x. TL;DR The grep included in busybox is painfully slow. When doing using grep to process lots of data, add a (real) grep to …

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