NDTS Gateway Installation

Gateway Installation

Prerequisites

• A Gateway UUID supplied by the NAN Repository administrator
• A Linux host (Ubuntu 20.04 or later recommended) that should be on the same network as the spectrometer workstations
• TCP port 60195 open inbound from those workstations

Installation Steps

# Copy the .gz file to the gateway computer
tar xf data-transport-gateway-<version>.tar.gz
cd dtgateway-installer
sudo ./install.sh
# → You will be prompted only for the Gateway UUID

Firewall

Open TCP port 60195 on the Gateway to all spectrometer workstations; no other inbound ports are required.

Verifying the Service

Note that the installer automatically runs systemctl start data-transport-gateway after installation, but it is always good to check when installing the software that the service started.

sudo systemctl status data-transport-gateway      # should show “active (running)”
sudo systemctl start  data-transport-gateway      # start if not running

Updating the Gateway

When installing the Gateway software the installation will auto-detect if another version exists. The installation will proceed as above, but without questions as it will find the previous configuration file and use those values.

# Run the same installer script from a newer package
cd dtgateway-installer
sudo ./install.sh             # auto-detects an existing install; no prompts

Note that the installer automatically runs systemctl restart data-transport-gateway after upgrading, but it is always good to check when installing the software that the service started. See Verifying the Service for details

Uninstalling the Gateway

Download the latest version of the Gateway software, unpack, and run the uninstall.sh script

sudo ./uninstall.sh           # script is included inside every package

Rolling Back the Gateway

Obtain the desired older package and run its install.sh

Rolling back more than one version is not recommended.

NDTS Gateway Configuration

The following are optional configuration values that can be specified in the /opt/nandt- gateway/gateway_configuration.json file. The file must adhere to proper JSON formatting:

Configuration Options

Option	Description	Default
log_file_path	Path to write the gateway log file	/opt/nandt-gateway/nan-gateway.log
logging_level	Minimum severity written to the log (fatal → debug)	info
logging_format	Python logging format string for each line	%(asctime)s %(levelname)s %(module)s [%(process)d]: %(message)s
base_output_path	Directory used for incoming experiment data	/opt/nandt-gateway/data/received
https_endpoint	HTTPS endpoint of the NDTS Receiver	https://receiver.usnan.org
retry_limit	Attempts to forward each dataset to the Receiver	5
retry_delay	Seconds to wait between retry attempts	300
rsync_username	SSH/rsync account on the Receiver	nandt
rsync_node	Node to which experiment files are rsync’d	receiver.usnan.org
request_queue_size	Outstanding daemon connections accepted before new ones are rejected. Increase this value if the gateway is rejecting requests from spectrometers evident in the workstation daemon log file showing network communication errors	50

Example JSON configuration file

{
  "log_file_path": "/opt/nandt-gateway/nan-gateway.log",
  "logging_level": "info",
  "logging_format": "%(asctime)s %(levelname)s %(module)s [%(process)d]: %(message)s",
  "base_output_path": "/opt/nandt-gateway/data/received",
  "https_endpoint": "https://receiver.usnan.org",
  "retry_limit": 5,
  "retry_delay": 300,
  "rsync_username": "nandt",
  "rsync_node": "receiver.usnan.org",
  "request_queue_size": 50
}

Logging Levels

Nothing below the set log level will be logged.

Level	Description	verbosity	default
fatal	Critical events only	very low
error	Problems that must be addressed for normal operation	low
warning	Unusual events that generally require no action	medium
info	Unusual or noteworthy events (recommended for production)	high	yes
debug	Detailed diagnostic messages useful for troubleshooting, but should not be left on for normal operation	extremely high

NDTS Gateway Components

The NDTS Gateway consists of several key components installed under /opt/nandt-gateway, unless otherwise noted. Each plays a specific role in data transfer, configuration, or monitoring.

File or Directory	Description
main.py	Entry point for the gateway's Python-based service
/etc/systemd/system/data-transport-gateway.service	systemd unit file used to control the gateway service
nan-gateway.log	Runtime log file (location can be changed via log_file_path in config)
gateway_configuration.json	Gateway configuration file containing operational parameters
data/received/	Temporary storage location for incoming dataset files until data is successfully forwarded to the receiver
data/retransmitter.pid	Contains the PID of the process that is attempting to re-send data that previously failed to be sent to the receiver. This is used internally by the gateway software to manage retransmitting data
data/users.dat	Cached list of user/sample/project/study data pulled from the receiver
data/user_checksum.dat	Checksum file used to determine when the users.dat file should be refreshed

All other files int the nandt-gateway directory are for the operation of the gateway, and are not of general interest

Normal Operation of the Gateway

Experiment Data Flow

• The gateway listens on its server port for connections from an NDTS daemon
• When a daemon indicates it has experiment data, the gateway opens a dedicated socket and saves the incoming files to the base output path (default /opt/nandt-gateway/data/received)
• After a complete, error-free transfer, the daemon marks the experiment as sent and will not resend it
• The gateway immediately spawns a Transmitter process—one per experiment—to forward the files to the NDTS Receiver
• A Transmitter retries up to retry_limit times, waiting retry_delay seconds between attempts
• On success, the experiment directory is deleted from the base output path; on exhaustion of retries the Transmitter exits and the data become eligible for Retransmit

Retransmit

• At start-up and after each heartbeat (see below), the gateway launches a Retransmitter
• The Retransmitter scans …/data/received for unsent experiments
• For any experiment whose original retry window has elapsed, it spawns a new Transmitter and repeats the transmit workflow until success or manual deletion
• Before creating a Retransmitter, the gateway checks for {base_output_path}/../retransmitter.pid; if that PID is active, no new Retransmitter is started

Heartbeat Forwarding

• The gateway does not send independent heartbeats
• Upon receiving a daemon heartbeat, it spawns a Heartbeat Transmitter that forwards the message to the NDTS Receiver, appending:

 * Local datetime  
 * UTC datetime  
 * Gateway UUID  

• If transmission fails, the heartbeat is dropped and the Heartbeat Transmitter exits

User-List Refresh

• Every 15 seconds the gateway spawns a Refresh Users process to request an updated user list (users, samples, projects, studies, etc.) from the Receiver
• The request includes the checksum stored in {base_output_path}/../user_checksum.dat
• If the checksum is outdated, the Receiver returns a new list, which the gateway saves to {base_output_path}/../users.dat and updates the checksum file
• When an NDTS daemon requests the user list, the gateway compares checksums; if they differ, it sends the current users.dat contents to the daemon

NDTS Gateway Logging

Logging level are controlled by the logging_level parameter in the JSON configuration file (see above)

Example log excerpt:

2022-06-06 09:22:23,130 INFO main [61393]: Starting gateway retransmitter instance...
2022-06-06 09:22:23,130 INFO main [61393]: Experiment file path = /opt/nandt-gateway/data/received
2022-06-06 09:22:23,132 INFO main [61393]: Starting gateway receiver network endpoint...
2022-06-06 09:22:23,133 INFO GatewayReceiver [61393]: Starting file receiver...
2022-06-06 09:22:23,133 INFO GatewayRetransmitter [61405]: In GatewayRetransmit handle() method...
2022-06-06 09:22:23,134 INFO GatewayRetransmitter [61405]: No experiments to retransmit -- exiting...
2022-06-06 09:22:23,134 INFO GatewayRetransmitter [61405]: GatewayRetransmit handle() method completed...
2022-06-06 09:23:12,829 INFO GatewayTransmitter [61512]: Heartbeat sent to https://receiver.usnan.org/heartbeat

From the log file note:

• The first three lines show the spawning of the retransmitter.
• The line that starts with “INFO GatewayReceiver” shows the file receiver starting, which means that it is awaiting connects from NDTS Daemons.
• The lines that contain “INFO GatewayRetransmitter” show that there are no experiments to retransmit, so the retransmitter exits.
• The last line shows that a heartbeat came in from an NDTS Daemon, and the Gateway is forwarding it to the Receiver.