Skip to content

Latest commit

 

History

History
64 lines (50 loc) · 3.16 KB

follower_node.md

File metadata and controls

64 lines (50 loc) · 3.16 KB
Raw

Follower Node

When started with "EnableFollowMode": true, algod starts with a special property which allows it to be paused. This allows software to be written which runs synchronously with a node. If you need account balances at each round, or at a particular round, this is the only way to do it. On start the node will be paused, the REST API is used to resume and select a new round.

It also allows fetching a Ledger State Delta object for recent rounds. This object is not designed for external users, but may be useful for advanced applications if you're willing to figure things out. It contains complete information for transitioning a database to the next round, including new account balances, changes to application and asset states, and new box information. Such information was previously unavailable to application developers.

This mode has a number of restrictions, which are described below.

Follower mode was initially created to be a data source for Conduit.

Configuration

Behavior is controlled with the config.json file:

property description
EnableFollowMode When set to true the node starts as a network follower.
MaxAcctLookback The number of additional Ledger State Delta objects available. The default can be used, increasing to 64 or higher could help performance.
CatchupParallelBlocks The number of blocks that are fetched concurrently. The default can be used, increasing to 64 or higher could help performance.

Usage

On startup, a follower node will be paused (synchronized) with its ledger's current round. For a new deployment configured as a follower node, the initial sync round is 0. When a sync round is set, the node advances MaxAcctLookback-1 rounds. The node is synchronized for the availability of Ledger State Delta data. This means the minimum sync round is provided and the node advances to cache future rounds.

New public endpoints are available to control the sync round:

  • GET /v2/ledger/sync - fetch the current sync round.
  • DELETE /v2/ledger/sync - resume normal catchup by deleting the sync round.
  • POST /v2/ledger/sync/{round} - set the sync round.

The Ledger State Delta is not designed for external consumption, but may still be useful for advanced applications. When the sync round is set, this endpoint can be used to fetch the Ledger State Delta for that round and up to MaxAcctLookback - 1 ahead of it:

  • GET /v2/deltas/{round} - Fetch the raw Ledger State Delta, optionally provide format=msgp for the internal msgp encoded object.

Restrictions

The follower node was stripped of all functionality not directly related to assisting with data-gathering capabilities. Since it is designed to run alongside another application, it was made as lightweight as possible. Other restrictions relate to the fact that this node is designed to be paused. So there are no guarantees that its internal state matches the current round of consensus.

In particular, the follower node cannot participate in consensus or send transactions to the network. Any attempt to register participation keys or submit transactions will be rejected.