INTERVIEW TASK FOR THE ROLE OF DevOps Engineer

Introduction

This task goes over some fundamentals of the operating Chainlink nodes and alerting systems:

• following open source documentation
• setting up software using Docker, Docker Compose
• configuring different modules to work with each other,
• interacting with the blockchain network through transactions

Aim

Use Chainlink software to provide ETH/USD price data to a new smart contract running on the Ethereum Sepolia testnet, making sure your infrastructure and node are monitored properly with Grafana and alerted upon with Alertmanager.

Requirements

• Set up a Chainlink node that communicates with the Ethereum Sepolia testnet
• Use an appropriate blockchain wallet (eg Metamask) to deploy a smart contract on the testnet, which can then be paid 1 testnet LINK payment to request the latest ETH/USD price from your Chainlink node. The Chainlink node should reply with a transaction to fulfill the request.
• Create a Grafana dashboard to monitor the following:
  • % HDD usage of VM
  • Chainlink node's account balance
• Set up an Alertmanager alert rule to send an email when the Chainlink node's balance goes below 0.5 ETH (the email settings may be dummy data)
• Use docker-compose to deploy all the required service

Installation

Docker

Uninstall old versions

Before you can install Docker Engine, you need to uninstall any conflicting packages.

Distro maintainers provide unofficial distributions of Docker packages in APT. You must uninstall these packages before you can install the official version of Docker Engine.

for pkg in docker.io docker-doc docker-compose docker-compose-v2 podman-docker containerd runc; do sudo apt-get remove $pkg; done

Install using the apt repository

Before you install Docker Engine for the first time on a new host machine, you need to set up the Docker repository. Afterward, you can install and update Docker from the repository.

1. Set up Docker's apt repository.

   # Add Docker's official GPG key:
    sudo apt-get update
    sudo apt-get install ca-certificates curl
    sudo install -m 0755 -d /etc/apt/keyrings
    sudo curl -fsSL https://download.docker.com/linux/ubuntu/gpg -o /etc/apt/keyrings/docker.asc
    sudo chmod a+r /etc/apt/keyrings/docker.asc
   
    # Add the repository to Apt sources:
    echo \
      "deb [arch=$(dpkg --print-architecture) signed-by=/etc/apt/keyrings/docker.asc] https://download.docker.com/linux/ubuntu \
      $(. /etc/os-release && echo "$VERSION_CODENAME") stable" | \
      sudo tee /etc/apt/sources.list.d/docker.list > /dev/null
    sudo apt-get update

2. Install the Docker packages.

   To install the latest version, run:

   sudo apt-get install docker-ce docker-ce-cli containerd.io docker-buildx-plugin docker-compose-plugin

Docker Compose

Update the package index, and install the latest version of Docker Compose:

sudo apt-get update
sudo apt install docker-compose

Add your user to the docker group.

Append the your user to the docker group to be able to interact with the Docker daemon without needing to use sudo for every Docker command

sudo usermod -aG docker $USER

Log out and log back in so that your group membership is re-evaluated

Run the Docker-compose

Be sure you are in chainlink-sepolia directory

docker-compose up -d

You can now connect to your Chainlink node's UI interface by navigating to http://localhost:6688. API credentials are stored in chainlink-volume/.api.

If you are using a VPS, you can create an SSH tunnel to your node for 6688:localhost:6688 to enable connectivity to the GUI. Typically this is done with ssh -i $KEY $USER@$REMOTE-IP -L 6688:localhost:6688 -N.

ETH/USD Price Feed

Requirements

• Fund the Ethereum address that your Chainlink node uses. You can find the address in the node Operator GUI under the Key Management configuration.

Setup your Operator contract

Deploy your own Operator contract

1. Go to Remix and open the Operator.sol smart contract.

2. On the Compile tab, click the Compile button for Operator.sol. Remix automatically selects the compiler version and language from the pragma line unless you select a specific version manually.

3. On the Deploy and Run tab, configure the following settings:

   • Select "Injected Provider" as your Environment. The Javascript VM environment cannot access your oracle node. Make sure your Metamask is connected to Sepolia testnet.

   • Select the "Operator" contract from the Contract menu.

   • Copy the LINK token contract address for the network you are using and paste it into the LINK field next to the Deploy button. For Sepolia, you can use this address:

     0x779877A7B0D9E8603169DdbD7836e478b4624789
     

   • Copy the Admin wallet address into the OWNER field.

   

4. Click transact. MetaMask prompts you to confirm the transaction.

5. If the transaction is successful, a new address displays in the Deployed Contracts section.

   

6. Keep note of the Operator contract address. You need it later for your consuming contract.

Whitelist your node address in the Operator contract

1. In the Chainlink node GUI, find and copy the address of your chainlink node.

2. In Remix, call the setAuthorizedSenders function with the address of your node. Note the function expects an array.

   

3. Click the transact function to run it. Approve the transaction in MetaMask and wait for it to confirm on the blockchain.

4. Call isAuthorizedSender function with the address of your node to verify that your chainlink node address can call the operator contract. The function must return true.

   

Add a job to the node

1. In the Chainlink Operator UI on the Jobs tab, click New Job.
2. Paste the job specification from above into the text field.

# THIS IS EXAMPLE CODE THAT USES HARDCODED VALUES FOR CLARITY.
# THIS IS EXAMPLE CODE THAT USES UN-AUDITED CODE.
# DO NOT USE THIS CODE IN PRODUCTION.

name = "Get > Uint256 - (TOML)"
schemaVersion = 1
type = "directrequest"
# evmChainID for Sepolia Testnet
evmChainID = "11155111"
# Optional External Job ID: Automatically generated if unspecified
# externalJobID = "b1d42cd5-4a3a-4200-b1f7-25a68e48aad8"
contractAddress = "YOUR_OPERATOR_CONTRACT_ADDRESS"
maxTaskDuration = "0s"
minIncomingConfirmations = 0
observationSource = """
    decode_log   [type="ethabidecodelog"
                  abi="OracleRequest(bytes32 indexed specId, address requester, bytes32 requestId, uint256 payment, address callbackAddr, bytes4 callbackFunctionId, uint256 cancelExpiration, uint256 dataVersion, bytes data)"
                  data="$(jobRun.logData)"
                  topics="$(jobRun.logTopics)"]

    decode_cbor  [type="cborparse" data="$(decode_log.data)"]
    fetch        [type="http" method=GET url="$(decode_cbor.get)" allowUnrestrictedNetworkAccess="true"]
    parse        [type="jsonparse" path="$(decode_cbor.path)" data="$(fetch)"]

    multiply     [type="multiply" input="$(parse)" times="$(decode_cbor.times)"]

    encode_data  [type="ethabiencode" abi="(bytes32 requestId, uint256 value)" data="{ \\"requestId\\": $(decode_log.requestId), \\"value\\": $(multiply) }"]
    encode_tx    [type="ethabiencode"
                  abi="fulfillOracleRequest2(bytes32 requestId, uint256 payment, address callbackAddress, bytes4 callbackFunctionId, uint256 expiration, bytes calldata data)"
                  data="{\\"requestId\\": $(decode_log.requestId), \\"payment\\":   $(decode_log.payment), \\"callbackAddress\\": $(decode_log.callbackAddr), \\"callbackFunctionId\\": $(decode_log.callbackFunctionId), \\"expiration\\": $(decode_log.cancelExpiration), \\"data\\": $(encode_data)}"
                  ]
    submit_tx    [type="ethtx" to="YOUR_OPERATOR_CONTRACT_ADDRESS" data="$(encode_tx)"]

    decode_log -> decode_cbor -> fetch -> parse -> multiply -> encode_data -> encode_tx -> submit_tx
"""

3. Replace YOUR_OPERATOR_CONTRACT_ADDRESS with the address of your deployed operator contract address from the previous steps.

4. Click Create Job. If the node creates the job successfully, a notice with the job number appears.

5. Click the job number to view the job details. You can also find the job listed on the Jobs tab in the Node Operators UI. Save the externalJobID value because you will need it later to tell your consumer contract what job ID to request from your node.

   

Create a request to your node

After you add jobs to your node, you can use the node to fulfill requests. This section shows what a requester does when they send requests to your node. It is also a way to test and make sure that your node is functioning correctly.

1. Open ATestnetConsumer.sol in Remix.

2. Note that setChainlinkToken(0x779877A7B0D9E8603169DdbD7836e478b4624789) is configured for Sepolia.

3. On the Compiler tab, click the Compile button for ATestnetConsumer.sol.

4. On the Deploy and Run tab, configure the following settings:

   • Select Injected Provider as your environment. Make sure your metamask is connected to Sepolia.
   • Select ATestnetConsumer from the Contract menu.

5. Click Deploy. MetaMask prompts you to confirm the transaction.

6. Fund the contract by sending LINK to the contract's address. See the Fund your contract page for instructions. The address for the ATestnetConsumer contract is on the list of your deployed contracts in Remix. You can fund your contract with 1 LINK.

7. After you fund the contract, create a request. Input your operator contract address and the job ID for the Get > Uint256 job into the requestEthereumPrice request method without dashes. The job ID is the externalJobID parameter, which you can find on your job's definition page in the Node Operators UI.

   

8. Click the transact button for the requestEthereumPrice function and approve the transaction in Metamask.

9. After the transaction processes, you can see the details for the complete the job run the Runs page in the Node Operators UI.

   

10. In Remix, click the currentPrice variable to see the current price updated on your consumer contract.

Credentials and Links

Chainlink

Email: [email protected]

Password: simplytaskapi1234

Grafana

localhost:3000

Dashboard

Username: admin

password: grafana

Prometheus

localhost:9090

Alertmanager

localhost:9093

Explorer Links

Oracle smart contract address

Chainlink node account address

Transaction hashes of data request and response

Open Source Documentation Contribution

I noticed a mising part in the Chainlink documentation. Fixed it and send a PR