Clio

Clio is an XRP Ledger API server. Clio is optimized for RPC calls, over WebSocket or JSON-RPC. Validated historical ledger and transaction data are stored in a more space-efficient format, using up to 4 times less space than rippled. Clio can be configured to store data in Apache Cassandra or ScyllaDB, allowing for scalable read throughput. Multiple Clio nodes can share access to the same dataset, allowing for a highly available cluster of Clio nodes, without the need for redundant data storage or computation.

Clio offers the full rippled API, with the caveat that Clio by default only returns validated data. This means that ledger_index defaults to validated instead of current for all requests. Other non-validated data is also not returned, such as information about queued transactions. For requests that require access to the p2p network, such as fee or submit, Clio automatically forwards the request to a rippled node and propagates the response back to the client. To access non-validated data for any request, simply add ledger_index: "current" to the request, and Clio will forward the request to rippled.

Clio does not connect to the peer-to-peer network. Instead, Clio extracts data from a group of specified rippled nodes. Running Clio requires access to at least one rippled node from which data can be extracted. The rippled node does not need to be running on the same machine as Clio.

Requirements

1. Access to a Cassandra cluster or ScyllaDB cluster. Can be local or remote.

2. Access to one or more rippled nodes. Can be local or remote.

Building

Clio is built with CMake. Clio requires at least GCC-11 (C++20), and Boost 1.75.0 or later.

Use these instructions to build a Clio executable from the source. These instructions were tested on Ubuntu 20.04 LTS.

# Install dependencies
  sudo apt-get -y install git pkg-config protobuf-compiler libprotobuf-dev libssl-dev wget build-essential bison flex autoconf cmake

# Compile Boost
  wget -O $HOME/boost_1_75_0.tar.gz https://boostorg.jfrog.io/artifactory/main/release/1.75.0/source/boost_1_75_0.tar.gz
  tar xvzf $HOME/boost_1_75_0.tar.gz
  cd $HOME/boost_1_75_0
  ./bootstrap.sh
  ./b2 -j$(nproc)
  echo "export BOOST_ROOT=$HOME/boost_1_75_0" >> $HOME/.profile && source $HOME/.profile

# Clone the Clio Git repository & build Clio
  cd $HOME
  git clone https://github.com/XRPLF/clio.git
  cd $HOME/clio
  cmake -B build && cmake --build build --parallel $(nproc)

Running

./clio_server config.json

Clio needs access to a rippled server. The config files of rippled and Clio need to match in a certain sense. Clio needs to know:

• the IP of rippled
• the port on which rippled is accepting unencrypted WebSocket connections
• the port on which rippled is handling gRPC requests

rippled needs to open:

• a port to accept unencrypted websocket connections
• a port to handle gRPC requests, with the IP(s) of Clio specified in the secure_gateway entry

The example configs of rippled and Clio are setups such that minimal changes are required. When running locally, the only change needed is to uncomment the port_grpc section of the rippled config. When running Clio and rippled on separate machines, in addition to uncommenting the port_grpc section, a few other steps must be taken:

1. change the ip of the first entry of etl_sources to the IP where your rippled server is running
2. open a public, unencrypted WebSocket port on your rippled server
3. change the IP specified in secure_gateway of port_grpc section of the rippled config to the IP of your Clio server. This entry can take the form of a comma-separated list if you are running multiple Clio nodes.

Once your config files are ready, start rippled and Clio. It doesn't matter which you start first, and it's fine to stop one or the other and restart at any given time.

Clio will wait for rippled to sync before extracting any ledgers. If there is already data in Clio's database, Clio will begin extraction with the ledger whose sequence is one greater than the greatest sequence currently in the database. Clio will wait for this ledger to be available. Be aware that the behavior of rippled is to sync to the most recent ledger on the network, and then backfill. If Clio is extracting ledgers from rippled, and then rippled is stopped for a significant amount of time and then restarted, rippled will take time to backfill to the next ledger that Clio wants. The time it takes is proportional to the amount of time rippled was offline for. Also be aware that the amount rippled backfills are dependent on the online_delete and ledger_history config values; if these values are small, and rippled is stopped for a significant amount of time, rippled may never backfill to the ledger that Clio wants. To avoid this situation, it is advised to keep history proportional to the amount of time that you expect rippled to be offline. For example, if you expect rippled to be offline for a few days from time to time, you should keep at least a few days of history. If you expect rippled to never be offline, then you can keep a very small amount of history.

Clio can use multiple rippled servers as a data source. Simply add more entries to the etl_sources section. Clio will load balance requests across the servers specified in this list. As long as one rippled server is up and synced, Clio will continue extracting ledgers.

In contrast to rippled, Clio will answer RPC requests for the data already in the database as soon as the server starts. Clio doesn't wait to sync to the network, or for rippled to sync.

When starting Clio with a fresh database, Clio needs to download a ledger in full. This can take some time, and depends on database throughput. With a moderately fast database, this should take less than 10 minutes. If you did not properly set secure_gateway in the port_grpc section of rippled, this step will fail. Once the first ledger is fully downloaded, Clio only needs to extract the changed data for each ledger, so extraction is much faster and Clio can keep up with rippled in real-time. Even under intense load, Clio should not lag behind the network, as Clio is not processing the data, and is simply writing to a database. The throughput of Clio is dependent on the throughput of your database, but a standard Cassandra or Scylla deployment can handle the write load of the XRP Ledger without any trouble. Generally the performance considerations come on the read side, and depends on the number of RPC requests your Clio nodes are serving. Be aware that very heavy read traffic can impact write throughput. Again, this is on the database side, so if you are seeing this, upgrade your database.

It is possible to run multiple Clio nodes that share access to the same database. The Clio nodes don't need to know about each other. You can simply spin up more Clio nodes pointing to the same database as you wish, and shut them down as you wish. On startup, each Clio node queries the database for the latest ledger. If this latest ledger does not change for some time, the Clio node begins extracting ledgers and writing to the database. If the Clio node detects a ledger that it is trying to write has already been written, the Clio node will backoff and stop writing. If later the Clio node sees no ledger written for some time, it will start writing again. This algorithm ensures that at any given time, one and only one Clio node is writing to the database.

It is possible to force Clio to only read data, and to never become a writer. To do this, set read_only: true in the config. One common setup is to have a small number of writer nodes that are inaccessible to clients, with several read only nodes handling client requests. The number of read only nodes can be scaled up or down in response to request volume.

When using multiple rippled servers as data sources and multiple Clio nodes, each Clio node should use the same set of rippled servers as sources. The order doesn't matter. The only reason not to do this is if you are running servers in different regions, and you want the Clio nodes to extract from servers in their region. However, if you are doing this, be aware that database traffic will be flowing across regions, which can cause high latencies. A possible alternative to this is to just deploy a database in each region, and the Clio nodes in each region use their region's database. This is effectively two systems.

Developing against rippled in standalone mode

If you wish you develop against a rippled instance running in standalone mode there are a few quirks of both clio and rippled you need to keep in mind. You must:

1. Advance the rippled ledger to at least ledger 256
2. Wait 10 minutes before first starting clio against this standalone node.

Logging

Clio provides several logging options, all are configurable via the config file and are detailed below.

log_level: The minimum level of severity at which the log message will be outputted. Severity options are trace, debug, info, warning, error, fatal.

log_to_console: Enable/disable log output to console. Options are true/false. Defaults to true.

log_directory: Path to the directory where log files are stored. If such directory doesn't exist, Clio will create it. If not specified, logs are not written to a file.

log_rotation_size: The max size of the log file in megabytes before it will rotate into a smaller file.

log_directory_max_size: The max size of the log directory in megabytes before old log files will be deleted to free up space.

log_rotation_hour_interval: The time interval in hours after the last log rotation to automatically rotate the current log file.

Note, time-based log rotation occurs dependently on size-based log rotation, where if a size-based log rotation occurs, the timer for the time-based rotation will reset.

Cassandra / Scylla Administration

Since Clio relies on either Cassandra or Scylla for its database backend, here are some important considerations:

• Scylla, by default, will reserve all free RAM on a machine for itself. If you are running rippled or other services on the same machine, restrict its memory usage using the --memory argument: https://docs.scylladb.com/getting-started/scylla-in-a-shared-environment/