Run a collator

Collators produce the blocks of the Robonomics parachain. This guide sets up a collator on a Linux server, registers it on chain and explains how it earns.

The source of this guide is the collator guide in the runtime repository.

What you need

A server: 8 CPU cores, 64 GB RAM, 2 TB NVMe. Such a server costs about $120–150 a month.
Disk: the parachain and the Polkadot relay chain together take about 1.1 TB and keep growing. Plan for at least 2 TB.
An account on Robonomics with more than 32 XRT free balance.

There is no Robonomics node binary. A collator runs Parity’s generic polkadot-omni-node with the Robonomics chain spec. The guide assumes a robonomics user with home /var/lib/robonomics/ and base path /var/lib/robonomics/base/.

Download polkadot-omni-node from the Polkadot SDK releases. Use the latest polkadot-stable* release; the commands below use polkadot-stable2609.

wget -O polkadot-omni-node \
  https://github.com/paritytech/polkadot-sdk/releases/download/polkadot-stable2609/polkadot-omni-node
chmod +x polkadot-omni-node
sudo mv polkadot-omni-node /usr/local/bin/

Download the chain spec:

wget -O /var/lib/robonomics/robonomics-polkadot.raw.json \
  https://raw.githubusercontent.com/airalab/robonomics/master/chain-spec/polkadot-parachain.raw.json

2. Generate the network key

The collator does not start without a network key:

polkadot-omni-node key generate-node-key \
  --base-path /var/lib/robonomics/base/ \
  --chain /var/lib/robonomics/robonomics-polkadot.raw.json

The key is written to /var/lib/robonomics/base/chains/robonomics/network/secret_ed25519. Back it up.

3. Start the node

Recommended ExecStart for a systemd service:

ExecStart=/usr/local/bin/polkadot-omni-node \
  --name "YOUR_NODE_NAME" \
  --chain /var/lib/robonomics/robonomics-polkadot.raw.json \
  --base-path /var/lib/robonomics/base/ \
  --collator \
  --sync warp \
  --telemetry-url "wss://telemetry.parachain.robonomics.network/submit/ 0" \
  -- \
  --sync warp

The first --sync warp is for the parachain. The one after -- is for the embedded relay chain. Without it, the relay chain can take weeks to sync.
The chain spec has no telemetry endpoint, so telemetry is enabled with --telemetry-url.

4. Generate session keys

Session keys are Aura (sr25519) keys. Start the node temporarily with --rpc-methods unsafe, then call author_rotateKeysWithOwner with your collator account:

curl -H "Content-Type: application/json" \
  -d '{"id":1,"jsonrpc":"2.0","method":"author_rotateKeysWithOwner","params":["YOUR_COLLATOR_ACCOUNT"]}' \
  http://127.0.0.1:9944

The result has two fields: keys and proof. Save both. Check that the node holds the keys:

curl -s -H "Content-Type: application/json" \
  -d '{"id":1,"jsonrpc":"2.0","method":"author_hasSessionKeys","params":["KEYS"]}' \
  http://127.0.0.1:9944

Then remove --rpc-methods unsafe and restart the node.

5. Register on chain

Send these extrinsics from your collator account, for example in Polkadot.js Apps:

session.setKeys(keys, proof) with the two values from the previous step. Do not pass an empty proof: the proof binds the keys to your account.
collatorSelection.registerAsCandidate(). This bonds 32 XRT.

Your node joins the set after a session change. A session is 3,600 blocks in the runtime, about 6 hours at 6-second blocks.

Check your candidacy on chain, not only by the node’s health: look at collatorSelection.candidateList and collatorSelection.invulnerables in Developer → Chain state.

The bond and the limits on candidates are runtime settings. Changing them needs a Root referendum. See XRT and governance.

How rewards work

A collator earns in two ways:

Block reward. A fixed 0.0042 XRT is minted directly to the author of every block. It has been in place since runtime 43.
Fees and tips. All fees and tips go to the collator pot. The author of a block receives a share of the pot.

The block reward is set to cover a server with a margin:

reward per block = (server cost per year × number of collators × 1.3)
                   / blocks per year / XRT price
                 = (2,040 × 7 × 1.3) / 4,505,143 / 1 ≈ 0.0042 XRT

The inputs are a $2,040-a-year server, 7 collators, a 30% margin and an XRT price of $1. The reward is revisited by runtime upgrade when the inputs change.

Your income depends on your share of the blocks: the more collators there are, the fewer blocks each one authors. Background and measurements: Collator rewards, measured.