Saturday, March 4, 2017

OpenShift, Docker, and Elasticsearch

***This is part of an ongoing series I call "Mode 1 Storage Guy goes to a Mode 2 World."  I'm not an expert (yet), YMMV.***

There are already many good setup docs for Elasticsearch on OpenShift, like here and here.  So what I'm going to do is flush out the concepts so those instructions make more sense.


OpenShift has a concept of a project.  This is how they provide multitenancy.

Next is namespace, which is similar to a project. 

Next is the image.  An image is a pre-packed container probably with an application installed, like MongoDB or JBOSS.  You can create new images by installing an application into a container and saving that container.  The image concept is analogous to a VM Template: you keep it updated and deploy fresh containers from it.

A stream seems to be a set of evolving images: for example, when you download the latest CentOS, you're not asking for a specific version, just the latest version.  The stream is the set of successive images that you get the latest from.

Application.  This is the normal definition of an application, however in the context of containers, it's good to think about the application as separate from a container

The catalog is a view, a view of the images held in the registry.

The registry is merely what OSE calls the collection of images, held in a folder.

A Pod is the OSE equivalent of a container

A deployment is the mechanism that manages where, how many, and replication on pods for a given application.

Persistent Volume Claim (PVC): In OpenShift, this is a request for storage.  It can sit unfulfilled.

Persistent Volume (PV): When you create a PVC, and then match it to a real LUN/Export, you have a PV.

Don't panic if you see the word "cartridge."  That's just British for container.

Some notes:
openshift's gui is very foreign. Take some time getting used to it.
Unless you're an old linux admin, you're going to need to take the linux learning curve seriously. You'll really need to brush up on vi, ls, cat, curl, and wget.
The & symbol is your friend.  For any command that appears hung (but isn't hung, it's actually running) like "docker run ", throw an '&' at the end and I betcha it'll give you your prompt back. 
I had no luck connecting to the OpenShift GUI via chrome, but firefox worked fine (remember, https and 8443)
When deploying images from docker into OpenShift, don't underestimate the Pull Secrets.  OpenShift has to be allowed to pull the images from Docker.  This mechanism is intended to prevent unauthorized access of Docker images.

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