Via as-config.yml an admin can configure sharding subdomains for each host or, per default, all hosts. example:

local-appsuite.com:
host: local-appsuite.com
shardingSubdomains: sharding.local-appsuite.com/appsuite/api
com.openexchange.cookie.domain.enabled: true
com.openexchange.cookie.domain: local-appsuite.com
com.openexchange.cookie.domain.prefixWithDot: true

The three additional parameters are necessary for correct cookie usage. The information is loaded into the users jslob on login. The UI uses this information to distribute image loading requests to the servers supplied. The parameter 'shardingSubdomains' accepts a single string with one subdomain and an array of subdomains. Example:

shardingSubdomains:
- sharding.local-appsuite.com/appsuite/api
- sharding2.local-appsuite.com/appsuite/api