Arvados

1. provide a python program that runs arv-keepdocker, looks for pairs like the ones below, and creates a tag link for each pair

wardv@shell.4xphq:~$ arv-keepdocker 
REPOSITORY                      TAG         IMAGE ID      COLLECTION                     CREATED             
arvados/jobs                    c1a8e01539932e2f0153cfb2ffc4eaa2c3dc00f1  sha256:eda7c  4xphq-4zz18-5cn1x9u4ki574i7    Mon Dec 19 16:25:22 2016
arvados/jobs                    c1a8e01539932e2f0153cfb2ffc4eaa2c3dc00f1  decde0035258  4xphq-4zz18-sr3yairajekj11z    Mon Dec 19 16:25:22 2016

2. update API server to check for those tag links when creating a new job or container request, so when someone asks for "decde0035258" or "4xphq-4zz18-sr3yairajekj11z" or {whatever 4xphq-4zz18-sr3yairajekj11z's PDH is}, it gets transparently rewritten to sha256:eda7c or {whatever 4xphq-4zz18-5cn1x9u4ki574i7's PDH is}.

Tag would look something like:

owner_uuid: zzzzz-tpzed-000000000000000
link_class: docker_image_migration
name: {whatever 4xphq-4zz18-sr3yairajekj11z's PDH is}
head_uuid: {whatever 4xphq-4zz18-5cn1x9u4ki574i7's PDH is}