Unofficial Docker Image For NiFi Registry

[Michal Klempa <mi...@gmail.com>]

Hi NiFi users,
let me modestly announce my unofficial Docker image I have built for
NiFi Registry:
https://hub.docker.com/r/michalklempa/nifi-registry

At first, I apologize for not contributing changes back into official
image. I have found that a bit complicated, given the number of
changes/enhancements I wanted to make to the docker image design. But
I have released everything under Apache License, so feel free to
re-use.

The image resolves a few problems with original docker image:
- https://issues.apache.org/jira/browse/NIFIREG-236 - External
configuration of docker container
  with michalklempa/nifi-registry you can override individual
configuration files and the startup scripts do not get into the way
(see https://github.com/michalklempa/docker-nifi-registry/#providing-configuration-by-mounting-files)
- https://issues.apache.org/jira/browse/NIFIREG-227 -
GitFlowPersistenceProvider option to clone repo on startup
  image is able to clone remote git repository at startup - either
using HTTPS or git+ssh scheme.
  this works with a great feature of upstream Registry:
https://issues.apache.org/jira/browse/NIFIREG-209 - Support rebuilding
metadata DB from Git repo. I was able to rebuilt the metadata database
from old git repository, using
michalklempa/nifi-registry:0.4.0-SNAPSHOT tag of the image.
- is based on alpine (smaller than the official one (251MB vs. 387MB).)
- option to enable Java Debug using env var
(https://github.com/michalklempa/docker-nifi-registry#standalone-instance-java-remote-debug)
- environment variable to set Xmx and Xms
(https://github.com/michalklempa/docker-nifi-registry#java-heap-options-and-other-properties-in-bootstrapconf)

Currently, the :latest tag points to 0.3.0-03, which is built from
0.3.0 release of NiFi Registry.
There is also a 0.4.0-SNAPSHOT tag, built from
https://github.com/apache/nifi-registry/commit/48cce8bad0e9f7d1b42030ffe352179bdd0f7fc3
which I will try to keep updated from master branch of upstream
version.

Any comments/testing/feedback/issues are welcome. Feel free to write
me an email, create an issue on github:
https://github.com/michalklempa/docker-nifi-registry

Looking forward to 0.4.0 release of NiFi Registry! Thanks to all
developers for this work.

Best,
Michal