# Deployment guide

This document explains the workflow to have a working group of drand nodes generate randomness. There are four sections to this guide:

  1. Generate the long-term key pairs and the group file.
  2. Start the daemons.
  3. Have each node collectively participate in the distributed key generation (DKG).
  4. Generate randomness.

# Setup

The setup process for a drand node consists of the following steps:

  1. Generate the long-term key pair for each node.
  2. Start the drand daemon on each node.
  3. The leader starts the command as a coordinator & every participant connects to the coordinator to setup the network.

This document explains how to do the setup with the drand binary itself. If you want to install drand using Docker, follow the Docker instructions instead.

# Long-term key

Each drand node needs a public and secret key to interact with the rest of the network. To generate these keys run drand generate-keypair followed by the address of your node:

drand generate-keypair drand.example.com

The address must be reachable over a TLS connection directly, or via a reverse proxy setup. If you need a non-secured channel, you can pass the --tls-disable flag, although this is not recommended. Disabling TLS should only really be done when running a development or test deployment.

The default location for your keys is ~/.drand. You can specify where you want the keys to be saved by using the --folder flag:

drand generate-keypair drand0.example.com --folder ~/.drand-node-0

# Starting drand daemon

The daemon does not automatically run in the background. To run the daemon in the background, you must add & to the end of your command. Docker users can use the -d option. Once the daemon is running, the best way to issue commands is to use the control functionalities. The control client has to run on the same server as the drand daemon, so only drand administrators can issue a command to their drand daemons.

To choose where drand listens, use the --private-listen flag. You can also use the --public-listen flag to specify the address of the public API. Both these flags allow specifying the interface and/or port for drand to listen on. The --private-listen flag is the primary listener used to expose a gRPC service for inter-group-member communication. The --public-listen flag exposes a public and limited HTTP service designed to be CDN friendly, and provide basic information for drand users.

The drand daemon can run using TLS, or using unencrypted connections. Drand tries to use TLS by default.

# With TLS

Drand nodes attempt to communicate by default over TLS-protected connections. Therefore, you need to point your node to the TLS certificate chain and corresponding private key you wish to use via:

drand start \
    --tls-cert <fullchain.pem> \
    --tls-key <privkey.pem>

To get TLS certificates for free, you can use, for example, Let's Encrypt with its official CLI tool EFF's certbot.

# TLS setup: Nginx with Let's Encrypt

Running drand behind a reverse proxy is the default method of deploying drand. Such a setup greatly simplifies TLS management issues (renewal of certificates, etc.). We provide here the minimum setup using Nginx and certbot - make sure you have both binaries installed with the latest version; Nginx version must be at least >= 1.13.10 for gRPC compatibility.

  1. First, add an entry in the Nginx configuration for drand:

    # /etc/nginx/sites-available/default
    server {
      server_name drand.example.xyz;
      listen 443 ssl http2;
    
      location / {
        grpc_pass grpc://localhost:4444;
        grpc_set_header X-Real-IP $remote_addr;
      }
    
      location /public/ {
        proxy_pass http://localhost:8080;
        proxy_set_header Host $host;
      }
      location /info {
        proxy_pass http://localhost:8080;
        proxy_set_header Host $host;
      }
      # Add ssl certificates by running certbot --nginx
    }
    

    You can change:

    1. the port on which you want drand to be accessible by changing the line listen 443 ssl http2 to use any port.
    2. the port on which the drand binary will listen locally by changing the line grpc_pass grpc://localhost:4444; to the private API port and proxy_pass http://localhost:8080; to the public API port.

    You can use different server blocks to apply different configurations (DNS names, for example) for the private and public API.

  2. Run certbot to get a TLS certificate:

    sudo certbot --nginx
    
  3. Running drand uses two ports: one for group member communication, and one for a public-facing API for distributing randomness. These ports and interfaces should be specified with flags.

    drand start --tls-disable --private-listen 127.0.0.1:4444 --public-listen drand0.example.com:8080
    

    The --private-listen flag tells drand to listen on the given address. The public-facing address associated with this listener is given to other group members in the setup phase (see below).

    If no private-listen address is provided, it will default to the discovered public address of the drand node.

    If no public-listen flag is provided, drand will not expose a public HTTP interface.

# TLS setup: Apache for HTTP

The equivalent Apache config block to the NGinX config above for forwarding HTTP requests back to the drand public port would be:

ProxyPreserveHost On
SSLProxyEngine on
SSLProxyCheckPeerCN off
ProxyPass / https://127.0.0.1:8080/
ProxyPassReverse / https://127.0.0.1:8080/
<Proxy *>
allow from all
</Proxy>

# Unencrypted-connections

Although we do not recommend turning off TLS, you can disable it by using the --tls-disable flag.

drand start --tls-disable

# Test the connection to a node

Use drand util check <address> to test the gRPC endpoint a drand node.

drand util check example.com

> drand: id example.com answers correctly

If the address used is a DNS name, this command will try to resolve the DNS name to IP. If you disabled TLS, you need to add the --tls-disable flag:

drand util check --tls-disable drand0.example.com

# Run the setup phase

To setup a new network, drand uses the notion of a coordinator that collects the public key of the participants, setups the group configuration once all keys are received, and then start the distributed key generation phase. Once the DKG phase is performed, the participants can see the list of members in the group configuration file.

Coordinator: The designated coordinator node must run the following command before everyone else:

drand share --leader --nodes 10 --threshold 6 --secret mysecret901234567890123456789012 --period 30s

Rest of participants: Once the coordinator has run the previous command, the rest of the participants must run the following command:

drand share --connect <leaderaddress> --secret mysecret901234567890123456789012

The flags usage is as follow:

Flag Description
--leader This node is the group coordinator.
--nodes The number of nodes in this group.
--threshold The minimum number of nodes that need to be online for the network to be live.
--period The period of the randomness beacon to use. It must be a valid duration as parsed by Golang's time.ParseDuration method.
--catchup-period The period of randomness when recovering from a failure. A valid Golang duration, it may be 0 to catch up as fast as possible.
--secret The password that the leader uses to authenticate nodes that want to participate in the group. This password must be at least 32 characters long.

The drand share command will run until the DKG has finished. If you quit the command, the DKG will continue, but the group file will not be created. In that case, once the DKG is done, you can get the group file by running:

drand show group --out group.toml

If you specified a --control in when you started the drand node, you will have to supply the same port with this command:

drand show group --out group.toml --control 3001

# Secret

As a basic security method, participants must include a shared secret before they can be accepted into a group. This secret is set by the leader. The secret must be at least 32 characters long. If the DRAND_SHARE_SECRET environment variable is set on your system, the command line flag can be omitted.

# Custom entropy source

Drand takes its entropy for the setup phase from the OS's entropy source by default. This source is /dev/urandom on Unix systems. However, it is possible for a participant to inject their own entropy source into the creation of their secret. To do so, you must have an executable that produces random data when called, and pass the name of that executable to drand:

drand share <regular options> --source <entropy-exec>

In this command, <entropy-exec> is the path to the executable, which produces the user's random data on STDOUT. As a precaution, the user's randomness is mixed by default with crypto/rand to create a random stream. In order to introduce reproducibility, the flag --user-source-only can be set to impose that only the user-specified entropy source is used. We recommend only using this flag during testing.

drand share <group-file> --source <entropy-exec> --user-source-only

# Group TOML file

Once the DKG phase is done, each node has both a private share and a group file containing the distributed public key. Using the previous commands, the group file will be written to group.toml. That updated group file is needed by drand to securely contact drand nodes on their public interface to gather private or public randomness. To view this file, run drand show group. If you want to save the output to a file, add the --out <file> flag:

drand show group --out ~/group-config.toml

# Randomness Generation

After a successful setup phase, drand will switch to the randomness generation mode at the genesis time specified in the group file. Each node broadcasts randomness shares at regular intervals. Every new random beacon is linked to the previous one in a chain of randomness. Once a node has collected a threshold of shares in the current round, it computes the public, random value, and stores it in its local instance of BoltDB.

For third party implementations of randomness beacon verification, you need:

  • The distributed public key generated during the setup phase.
  • The period.
  • The genesis time of the chain.

As an administrator of a drand node, you can use the control port to access the chain information:

drand show chain-info

Non-administrators can contact an external drand node to ask for its current distributed public key:

drand get chain-info <address>

In this command, <address> is the address of a drand node. Use the--tls-cert flag to specify the server's certificate if needed. The group.toml file does not need to be updated with the collective key.

When using the get chain-info method, a drand node can lie about the key if no out-of-band verification is performed. That information is usually best gathered from a trusted drand operator and then embedded in any applications using drand.

# Timings

At each new period, each node will try to broadcast their partial signatures for the corresponding round and try to generate full randomness from the partial signatures. The corresponding round is the number of rounds elapsed from the genesis time. That means there is a 1-1 mapping between a given time and a drand round.

# Daemon downtime and chain sync

Due to the threshold nature of drand, a drand network can support some numbers of nodes offline at any given point. This number is determined by the threshold: max_offline = group_len - threshold. When a drand node goes back up, it will sync rapidly with the other nodes to catch up its local chain and participate in the next upcoming drand round.

# Drand network failure

If, for some reason, drand goes down for some time and then backs up, the new random beacon will be built over the last successfully generated beacon. For example, if the network goes down at round 10 (i.e., the last beacon generated contained round: 10), and back up again at round 20 (i.e., field round: 20), then this new randomness contains the field previous_round:10.

# Control functionalities

Drand's local administrator interface provides further functionality, e.g., to update group details or retrieve secret information. By default, the daemon listens on 127.0.0.1:8888, but you can specify another control port when starting the daemon with:

drand start --control 1234

In that case, you need to specify the control port for each of the following commands.

# Long-term private key

To retrieve the long-term private key of our node, run:

drand show private

# Long-term public key

To retrieve the long-term public key of our node, run:

drand show public

# Private key share

To retrieve the private key share of our node, as determined during the DKG, run the following command:

drand show share

The JSON-formatted output has the following form:

{
  "index": 1,
  "share": {
    "gid": 22,
    "scalar": "764f6e3eecdc4aba8b2f0119e7b2fd8c35948bf2be3f87ebb5823150c6065764"
  }
}

The "gid" simply indicates which group the data belongs to. It is present for scalar and points on the curve, even though scalars are the same on the three groups of bls12-381. The field is present already to be able to accommodate different curves later on.

# Chain information

To retrieve information about the chain this node participates in, run:

drand show chain-info

# Updating drand group

Drand allows for "semi-dynamic" group update with a resharing protocol that offers the following:

  • New nodes can join an existing group and get new shares. Note that, in fact, all nodes get new shares after running the resharing protocol.
  • Nodes can leave their current group. It may be necessary for nodes that do not wish to operate drand anymore.
  • Nodes can update the threshold associated with their current distributed public key.
  • refresh the shares (similar to using a new private key)

The main advantage of this method is that the distributed public key stays the same even with new nodes coming in. That can be useful when the distributed public key is embedded inside the application using drand, and hence is difficult to update.

Setting up the coordinator: The coordinator must be a member of the current network. To run the coordinator, run the following:

drand share --leader --transition --secret mysecret901234567890123456789012 --nodes 15 --threshold 10 --out
group2.toml

Setting up the current members for the resharing: The current members can simply run the following command:

drand share --connect <coordinator> --transition --secret mysecret901234567890123456789012 --out group2.toml

Setting up the new members: The new members need the current group file to proceed. Check how to get the group file in the Deployment section.

TIP

A new member will need the full history of randomness beacons to participate in a group so that the new node can field requests for previous rounds. Getting the full history can take a while.

A new member can synchronize with a chain before joining. This can be done by anyone, and does not require resharing to have started.

drand follow --sync-nodes <cooridinator> --chain-hash <chain hash>

This command will not exit, but will keep adding new beacons to the local database as they are produced. If you wish for the command to terminate once it has synchronized up to now, you can add the option --up-to=<round> where round is the current randomness round.

To join the group, the incoming member should execute:

drand share connect <coordinator> --from group.toml --secret mysecret901234567890123456789012 --out group2.toml

After the protocol is finished, each node will have the new group file written out as group2.toml. The randomness generation starts only at the specified transition time specified in the new group file.

# Metrics

The --metrics <metrics-address> flag may be used to launch a metrics server at the provided address. The address may be specified as 127.0.0.1:port, or as :port to bind to the default network interface. The webserver at this port will serve pprof runtime profiling data at <metrics>/debug/pprof, allow triggering golang garbage collection at <metrics>/debug/gc, and will serve prometheus metrics at <metrics>:/metrics. Prometheus counters track the number of gRPC requests sent and received by the drand node, as well as the number of HTTP API requests. This endpoint should not be exposed publicly. If desired, prometheus metrics can be used as a data source for grafana dashboards or other monitoring services.