As a wcqs user I want to see a page informing me of data reload in progress, so that I know when service outage is done on purpose, or so that I don't get incomplete data.
AC:
Most of the internet recommends having a page that is renamed when maintenance is on and check for its filename for affected location. Another approach, would be to switch enabled sites. I prefer the second approach, since it doesn't affect the location during standard operation - although is more difficult to develop. First one would require a disk seek for each request.
The cost of checking the existence of a file on each request is irrelevant compared to the cost of a Blazegraph request, so that should not be an issue. It looks simpler to me than using site enabled, so I would go for it. This is also the solution we had previously on WDQS.
This is only a transitional solution (we'll have streaming updates at some point, and for a service behind LVS we will be able to depool a node), so we should go for the simpler solution and not overthink it now.
Change 619259 had a related patch set uploaded (by ZPapierski; owner: ZPapierski):
[operations/puppet@production] Replace a query service during data reload
Change 619260 had a related patch set uploaded (by ZPapierski; owner: ZPapierski):
[wikidata/query/rdf@master] Use maintenance page during data reload
Change 619260 merged by jenkins-bot:
[wikidata/query/rdf@master] Use maintenance page during data reload
Change 619259 merged by Ryan Kemper:
[operations/puppet@production] Replace a query service during data reload