The recent reindex that we tried to do on Commons failed twice, which delayed the rollout of features to users. One of those was a partial failure which is a total pain to fix properly. This is infrastructure worth investing in.

I wanted to use the reindex API wrote by Nik. It would greatly help to reduce code complexity in cirrus and hopefully have a more stable reindex process.
The reindex API supports a script param that would allow us to do update reindex docs (e.g. to populate the new wiki field).
Sadly with elastic 2.x the script language used is groovy and is disabled by default for security reasons.
We could add

script.engine.groovy.inline.update: true

to elasticsearch.yml to allow it.

With elasticsearch 5 we have access to painless a new script engine very similar to groovy that is enabled by default.

If we want to use the reindex API our options are:

1. Enable groovy
2. Wait for elasticsearch 5 and use painless

I'm still undecided, I'm not too keen enabling groovy, we've spent some effort to remove all groovy scripts from cirrus on the other hand reindexing is painful today...