Data flow control in distributed computing systems

Datacenters or other large-scale distributed computing systems can provide computing resources such as processing power and data storage as computing services accessible to tenants via a computer network. A tenant, such as a corporation, school, or organization, can have multiple users or groups of users with corresponding websites. To facilitate ready access, data relevant to a user, group, or website of a tenant can be stored in a dedicated network location sometimes referred to as a shard. A shard can be a physical and/or logical storage location that contains emails, chats, instant messages, documents, photos, videos, or other types of content items with which the user, group, or website can interact.