> For the complete documentation index, see [llms.txt](https://docs.polystream.xyz/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.polystream.xyz/project-architecture/cranker.md).
# Cranker
Cranker with chainlink automation upkeep
Chainlink Automation provides a decentralized network of automated agents (keepers) that trigger on-chain smart contract executions based on predefined conditions, eliminating manual intervention and operational risks.
#### Use Cases in Polystream
* **Epoch Management:**\
Automated triggering of epoch changes to handle yield harvesting, yield optimization, and state updates at consistent intervals.
* **Reward Distributions:**\
Automating distribution and accounting of accrued yield rewards at each epoch boundary to ensure timely and fair distribution.
### How it Works (Technical Flow)
1. **Condition Definition:**\
On-chain conditions (`checkUpkeep`) defined in the smart contract specify precisely when automation triggers should activate.
```solidity
solidityCopyEditfunction checkUpkeep(bytes calldata) external view returns (bool upkeepNeeded, bytes memory performData) {
upkeepNeeded = (block.timestamp >= lastEpochTime + EPOCH_DURATION);
}
```
2. **Automated Execution:**\
Once conditions are met, Chainlink Automation calls the `performUpkeep` function on your deployed contract:
```solidity
solidityCopyEditfunction performUpkeep(bytes calldata) external {
checkAndHarvest(); // Harvest yield and distribute rewards
optimizeYield(); // Automatically selects best yielding protocol
}
```
3. **$LINK Token Payments:**\
Each automation execution consumes Chainlink's `$LINK` tokens from the project's Automation balance, compensating the keepers for their service.
Chainlink Automation dashboard showing periodic performUpkeep executions and $LINK payments
---
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