💡
Note: In this example, we use a config.yml file with logging enabled, along with the node IP information and credentials.
### Subscribe RPC
When a client wants to receive specific state data, it initiates a subscription using the Subscribe RPC. This subscription includes one or more paths outlining the desired data, along with a chosen subscription mode. There are three modes that determine the duration of the subscription:
* **ONCE**: specifies a subscription that provides data as a one-time response
* **POLL**: is a subscription that uses a stream to periodically request data
* **STREAM**: is a continuous subscription that streams data based on triggers defined by the subscription mode. This mode can be `ON_CHANGE,` `SAMPLE`, or `TARGET_DEFINED`
**ONCE**
A subscription operating in the ONCE mode dictates a single request/response exchange
```python
gnmic -a 172.20.20.13:57400 -u admin -p codeNetwk@123! --insecure \
sub --path "/state/system/memory-pools/summary" -- mode once
{
"source": "172.20.20.13:57400",
"subscription-name": "default-1777327406",
"timestamp": 1777327406422019039,
"time": "2026-04-28T10:03:26.422019039+12:00",
"prefix": "state/system/memory-pools/summary",
"updates": [
{
"Path": "current-total-size",
"values": {
"current-total-size": "2095054848"
}
},
{
"Path": "total-in-use",
"values": {
"total-in-use": "1898836352"
}
},
{
"Path": "available-memory",
"values": {
"available-memory": "1720713216"
}
}
]
}
{
"sync-response": true
}
```
**STREAM**
Stream subscriptions are long-lived subscriptions which continue to transmit updates at the requested sample interval for the set of paths within the Subscribe Request indefinitely
```python
gnmic -a 172.20.20.13:57400 -u admin -p codeNetwk@123! --insecure \
sub --path "/state/port[port-id=1/1/c1/1]/statistics/in-packets" -- sample-interval 10s
{
"source": "172.20.20.13:57400",
"subscription-name": "default-1777327689",
"timestamp": 1777327689262295519,
"time": "2026-04-28T10:08:09.262295519+12:00",
"prefix": "state/port[port-id=1/1/c1/1]/statistics",
"updates": [
{
"Path": "in-packets",
"values": {
"in-packets": "14376890"
}
}
]
}
{
"sync-response": true
}
{
"source": "172.20.20.13:57400",
"subscription-name": "default-1777327689",
"timestamp": 1777327699260018112,
"time": "2026-04-28T10:08:19.260018112+12:00",
"prefix": "state/port[port-id=1/1/c1/1]/statistics",
"updates": [
{
"Path": "in-packets",
"values": {
"in-packets": "14376916"
}
}
]
}
{
"source": "172.20.20.13:57400",
"subscription-name": "default-1777327689",
"timestamp": 1777327709259895901,
"time": "2026-04-28T10:08:29.259895901+12:00",
"prefix": "state/port[port-id=1/1/c1/1]/statistics",
"updates": [
{
"Path": "in-packets",
"values": {
"in-packets": "14376945"
}
}
]
}
```
## Dial-out Telemetry
In general, the SR-OS node performs the role of a gRPC server responding to subscription requests from a gRPC client. However, it is possible for the SR-OS to perform the role of gRPC client, initiating gRPC connections and pushing data to a gRPC server using a Publish RPC. This is referred to as *dial-out telemetry*
Dial-out subscriptions are configured on the router and are persistent. The configuration is defined with three constituent parts;
* A ***sensor group*** to define one or more schema paths to stream
* A ***destination group*** specifying the destination address(es) and ports that the router uses to send telemetry data.
* ***Persistent subscriptions*** to associate a sensor group with a destination group
The following shows an example of the SR-OS configuration for dial-out telemetry.
```python
system {
telemetry {
destination-group "dialout" {
allow-unsecure-connection
destination 172.31.255.29 port 57400 {
router-instance "Base"
}
}
persistent-subscriptions {
subscription "dialout" {
admin-state enable
sensor-group "port-stats"
mode sample
destination-group "dialout"
encoding bytes
}
}
sensor-groups {
sensor-group "port-stats" {
path "/state/port[port-id=1/1/c1/1]/statistics/out-octets" { }
}
}
}
}
A:admin@PE1# /show system telemetry persistent subscription "dialout"
===============================================================
Telemetry persistent subscription
===============================================================
Subscription Name : dialout
Administrative State : Enabled
Operational State : Up
Subscription Id : 65
Description : (Not Specified)
Sensor Group : port-stats
Destination Group : dialout
Path Mode : sample
Sample Interval : 10000 ms
Encoding : json-ietf
===============================================================
```
### Setup gNMIc
To make gNMIc simulate a gRPC server, use the listen argument along with an IP address and port to receive publish subscriptions.
```python
gnmic listen -a 172.31.255.29:57400 --insecure
{
"source": "172.20.20.13:58158",
"system-name": "PE1",
"subscription-name": "dialout",
"timestamp": 1777328434091359417,
"time": "2026-04-28T10:20:34.091359417+12:00",
"prefix": "state/port[port-id=1/1/c1/1]/statistics",
"updates": [
{
"Path": "out-octets",
"values": {
"out-octets": "5521927017"
}
}
]
}
{
"source": "172.20.20.13:58158",
"system-name": "PE1",
"subscription-name": "dialout",
"timestamp": 1777328444090433719,
"time": "2026-04-28T10:20:44.090433719+12:00",
"prefix": "state/port[port-id=1/1/c1/1]/statistics",
"updates": [
{
"Path": "out-octets",
"values": {
"out-octets": "5521939044"
}
}
]
}
```
# The GPG Stack Architecture
The GPG Stack (GNMIC · Prometheus · Grafana) serves as a cloud-native observability pipeline for network telemetry. GNMIC connects the gNMI push model with Prometheus's pull-based scrape model.
![](https://cdn.hashnode.com/uploads/covers/68933f4690103a1d4a8d7df7/ee58d3f9-4150-4bc0-9155-337c4b0b6272.jpg align="center")
*Telemetry Stack*
## GNMIC Config — Prometheus Output Mode
```python
subscriptions:
port_stats_nokia:
paths:
- "/state/port[port-id=*]/statistics/in-packets"
- "/state/port[port-id=*]/statistics/out-packets"
- "/state/port[port-id=*]/statistics/in-octets"
- "/state/port[port-id=*]/statistics/out-octets"
mode: stream
stream-mode: sample
sample-interval: 10s
encoding: json_ietf
service_state:
paths:
- "/state/service/vprn[service-name=*]/oper-state"
mode: once
system_facts:
paths:
- "configure/system/name"
- "state/system/version"
mode: once
system_resources:
paths:
- "/state/system/memory-pools/summary"
- "/state/system/cpu[sample-period=60]/summary"
mode: stream
stream-mode: sample
sample-interval: 10s
encoding: json_ietf
targets:
172.20.20.13:
outputs:
prometheus-out:
type: prometheus
listen: ":9804"
path: /metrics
expiration: 10m
metric-prefix: sros_
```
### Run gNMIc
```python
gnmic --config configs/subscriptions.yml sub --name port_stats_nokia
# Confirm if metrics are being exposed to Prometheus
curl http://localhost:9804/metrics | head -20
sros__state_port_statistics_in_octets{port_port_id="1/1/c1",source="172.20.20.13",subscription_name="port_stats_nokia"} 0
sros__state_port_statistics_in_octets{port_port_id="1/1/c1/1",source="172.20.20.13",subscription_name="port_stats_nokia"} 5.510908681e+09
sros__state_port_statistics_in_octets{port_port_id="1/1/c2/1",source="172.20.20.13",subscription_name="port_stats_nokia"} 8.342930752e+09
sros__state_port_statistics_in_octets{port_port_id="1/1/c3/1",source="172.20.20.13",subscription_name="port_stats_nokia"} 149554
```
## Prometheus Configuration
Install [Prometheus](https://prometheus.io/docs/prometheus/latest/installation/)
`prometheus.yml`
```python
global:
scrape_interval: 15s
scrape_configs:
- job_name: 'gnmic'
static_configs:
- targets: ['localhost:9804']
```
### Access Prometheus
```python
http://localhost:9090
#If running on a VM (like your Rocky Linux setup)
http://