We have a variety of per-cluster options now (should be all consolidated into CirrusSearch\ClusterSettings by now):
$wgCirrusSearchDefaultCluster $wgCirrusSearchClusters $wgCirrusSearchShardCount $wgCirrusSearchReplicas $wgCirrusSearchClientSideConnectTimeout $wgCirrusSearchDropDelayedJobsAfter
Additionally there is one more new setting being added in https://gerrit.wikimedia.org/r/244247:
$wgCirrusSearchWriteClusters
We need to work up a patch that sets these all appropriately for the eqiad, codfw and labsearch clusters. This should be deployed after shipping gerrit 244247 with the list of clusters to write to (cherry-pick to prod seems easy enough if we can test and merge this wednesday-ish).