Observing Squad

The N+1 setup for connecting to the Elrond Network

In order to integrate with the Elrond Network and be able to broadcast transactions and query blockchain data in an optimized approach, one needs to setup an on-premises Observing Squad.

An Observing Squad is defined as a set of N Observer Nodes (one for each Shard, including the Metachain) plus an Elrond Proxy instance which will connect to these Observers and provide an HTTP API (by delegating requests to the Observers).

tip

Currently the Elrond Mainnet has 3 Shards, plus the Metachain. Therefore, the Observing Squad is composed of 4 Observers and one Proxy instance.

By setting up an Observing Squad and querying the blockchain data through the Proxy, the particularities of Elrond's sharded architecture are abstracted away. This means that the client interacting with the Proxy does not have to be concerned about sharding at all.

System requirements

The Observing Squad can be installed on multiple machines or on a single, but more powerful machine.

In case of a single machine, our recommendation is as follows:

  • 8 x CPU
  • 32 GB RAM
  • HDD that can grow up to 5TB
  • 100 Mbit/s always-on Internet connection
  • Linux OS (Ubuntu 18.04 recommended)

Setup via the Mainnet scripts

Installation and Configuration

The Observing Squad can be setup using the installation scripts. Within the installation process, the LookupDatabaseExtension feature (required by the Hyperblock API) will be enabled by default.

Clone the installer repository:

git clone https://github.com/ElrondNetwork/elrond-go-scripts-mainnet.git

Edit config/variables.cfg accordingly. For example:

CUSTOM_HOME="/home/ubuntu/ObservingSquad"
CUSTOM_USER="ubuntu"

Additionally, you might want to set the following option, so that the logs are saved within the logs folder of the node:

NODE_EXTRA_FLAGS="-log-save"

Run the installation script as follows:

./script.sh observing-squad

After installation, 5 new systemd units will be available (and enabled).

Start the nodes and the Proxy using the command:

./script.sh start

In order to check the status of the Observing Squad, please see the section Monitoring and trivial checks below.

Upgrading the Observing Squad

The Observing Squad can be updated using the Mainnet installation scripts.

January 2021 upgrade

In order to upgrade the Observing Squad - that is, both the Observers and the Proxy, one should issue the following commands:

$ cd ~/elrond-go-scripts-mainnet
$ ./script.sh github_pull
$ ./script.sh stop
$ ./script.sh upgrade_squad
$ ./script.sh upgrade_proxy
$ ./script.sh start
important

The observing squad must be upgraded before 26th of January 14:20 UTC. Otherwise, the nodes will lose sync.

Prerequisites for the November 2020 upgrade

Observing Squads set up before November 2020 have been installed using a special branch of the Mainnet installation scripts: exchanges-integration. This special branch has been removed, in favor of the main branch of the installation scripts.

In order to upgrade an Observing Squad set up before November 2020, one has to first follow these steps:

$ cd ~/elrond-go-scripts-mainnet
MANUALLY BACKUP FILE config/variables.cfg

# IN ORDER TO ALLOW THE SUBSEQUENT SWITCH TO MAIN BRANCH
$ git checkout config/variables.cfg
# SWITCH TO MAIN BRANCH
$ git checkout master

MANUALLY RESTORE FILE config/variables.cfg

After following the steps above, the upgrade procedure shall continue as described in the next section.

General upgrade procedure

In order to upgrade the Observing Squad - that is, both the Observers and the Proxy, one should issue the following commands:

$ cd ~/elrond-go-scripts-mainnet
$ ./script.sh github_pull
$ ./script.sh stop
$ ./script.sh upgrade_squad
$ ./script.sh upgrade_proxy
$ ./script.sh start

After running the commands above, the upgraded Observing Squad will start again. The expected downtime is about 2-3 minutes.

Monitoring and trivial checks

One can monitor the running Observers using the termui utility (installed during the setup process itself), as follows:

~/elrond-utils/termui --address localhost:8080    # Shard 0
~/elrond-utils/termui --address localhost:8081    # Shard 1
~/elrond-utils/termui --address localhost:8082    # Shard 2
~/elrond-utils/termui --address localhost:8083    # Metachain

Alternatively, one can query the status of the Observers by performing GET requests using curl:

curl http://localhost:8080/node/status | jq    # Shard 0
curl http://localhost:8081/node/status | jq    # Shard 1
curl http://localhost:8082/node/status | jq    # Shard 2
curl http://localhost:8083/node/status | jq    # Metachain

The Proxy does not offer a termui monitor, but its activity can be inspected using journalctl:

journalctl -f -u elrond-proxy.service

Optionally, one can perform the following smoke test in order to fetch the latest synchronized hyperblock:

export NONCE=$(curl http://localhost:8079/network/status/4294967295 | jq '.data["status"]["erd_highest_final_nonce"]')
curl http://localhost:8079/hyperblock/by-nonce/$NONCE | jq

Setup via Docker

One can set up an Observing Squad using Docker, as described here. The images (for the Proxy and for the Observers) are published on Docker Hub.

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