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gNMI Server#

Introduction#

On top of acting as gNMI client gNMIc can run a gNMI server that supports Get, Set and Subscribe RPCs.

The goal is to act as a caching point for the collected gNMI notifications and make them available to other collectors via the Subscribe RPC.

Using this gNMI server feature it is possible to build gNMI based clusters and pipelines with gNMIc.

The server keeps a cache of the gNMI notifications received from the defined subscriptions and utilizes it to build the Subscribe RPC responses.

The unary RPCs, Get and Set, are relayed to known targets based on the Prefix.Target field.

Supported features#

  • Supports gNMI RPCs, Get, Set, Subscribe
  • Acts as a gNMI gateway for Get and Set RPCs.
  • Supports Service registration with Consul server.
  • Supports all types of gNMI subscriptions, once, poll, stream.
  • Supports all types of stream subscriptions, on-change, target-defined and sample.
  • Supports updates-only with stream and once subscriptions.
  • Supports suppress-redundant.
  • Supports heartbeat-interval with on-change and sample stream subscriptions.

Get RPC#

The server supports the gNMI Get RPC, it allows a client to retrieve gNMI notifications from multiple targets into a single GetResponse.

It relies on the GetRequest Prefix.Target field to select the target(s) against which it will run the Get RPC.

If Prefix.Target is left empty or is equal to *, the Get RPC is performed against all known targets. The received GetRequest is cloned, enriched with each target name and sent to the corresponding destination.

Comma separated target names are also supported and allow to select a list of specific targets to send the Get RPC to.

gnmic -a gnmic-server:57400 get --path /interfaces \
                                --target router1,router2,router3

Once all GetResponses are received back successfully, the notifications contained in each GetResponse are combined into a single GetResponse with each notification's Prefix.Target populated, if empty.

The resulting GetResponse is then returned to the gNMI client. If one of the RPCs fails, an error with status code Internal(13) is returned to the client.

If the GetRequest Path has the Origin field set to gnmic, the request is performed against the internal gNMIc server configuration. Currently only the paths targets and subscriptions are supported.

gnmic -a gnmic-server:57400 get --path gnmic:/targets
gnmic -a gnmic-server:57400 get --path gnmic:/subscriptions

Set RPC#

This gNMI server supports the gNMI Set RPC, it allows a client to run a single Set RPC against multiple targets.

Just like in the case of Get RPC, the server relies on the Prefix.Target field to select the target(s) against which it will run the Set RPC.

If Prefix.Target is left empty or is equal to *, a Set RPC is performed against all known targets. The received SetRequest is cloned, enriched with each target name and sent to the corresponding destination.

Comma separated target names are also supported and allow to select a list of specific targets to send the Set RPC to.

gnmic -a gnmic-server:57400 set \
        --update /system/ssh-server/admin-state:::json:::disable \
        --target router1,router2,router3

Once all SetResponses are received back successfully, the UpdateResults from each response are merged into a single SetResponse, with the addition of the target name set in Path.Target.

Note

Adding a target value to a non prefix path is not compliant with the gNMI specification which stipulates that the Target field should only be present in Prefix Paths

The resulting SetResponse is then returned to the gNMI client. If one of the RPCs fails, an error with status code Internal(13) is returned to the client.

Subscribe RPC#

The gNMIc server keeps a cache of gNMI notifications synched with the configured targets based on the configured subscriptions.

The Subscribe requests received from a client are run against the afore mentioned cache, this means that a client cannot get updates about a leaf that gNMIc did not subscribe to as a client.

Clients can subscribe to specific target using the gNMI Prefix.Target field, while leaving the Prefix.Target field empty or setting it to * is equivalent to subscribing to all known targets.

Subscription Mode#

gNMIc gNMI Server supports the 3 gNMI specified subscription modes: Once, Poll and Stream.

It also supports some subscription behavior modifiers:

  • updates-only with stream and once subscriptions.
  • suppress-redundant.
  • heartbeat-interval with on-change and sample stream subscriptions.

Once#

A subscription operating in the ONCE mode acts as a single request/response channel. The target creates the relevant update messages, transmits them, and subsequently closes the RPC.

In this subscription mode, gNMIc server supports the updates-only knob.

Poll#

Polling subscriptions are used for on-demand retrieval of data items via long-lived RPCs. A poll subscription relates to a certain set of subscribed paths, and is initiated by sending a SubscribeRequest message with encapsulated SubscriptionList. Subscription messages contained within the SubscriptionList indicate the set of paths that are of interest to the polling client.

Stream#

Stream subscriptions are long-lived subscriptions which continue to transmit updates relating to the set of paths that are covered within the subscription indefinitely.

In this subscription mode, gNMIc server supports the updates-only knob.

On Change#

When a subscription is defined to be on-change, data updates are only sent to the client when the value of the data item changes.

In the case of gNMIc gNMI server, on-change subscriptions depend on the subscription writing data in the local cache, if it is a sample subscription, each update from a target will trigger an on-change update to the server client.

gNMIc gNMI server supports on-change subscriptions with heartbeat-interval. If the heartbeat-interval value is set to a non zero value, the value of the data item(s) MUST be re-sent once per heartbeat interval regardless of whether the value has changed or not.

Note

The minimum heartbeat-interval is configurable using the field min-heartbeat-interval. It defaults to 1s

If the received heartbeat-interval value is greater than zero but lower than min-heartbeat-interval, the min-heartbeat-interval value is used instead.

Target Defined#

When a client creates a subscription specifying the target defined mode, the target MUST determine the best type of subscription to be created on a per-leaf basis.

In the case of gNMIc gNMI server, a target-defined stream subscription, is treated as an on-change subscription.

Note that this does not mean that gNMIc will filter out the unchanged values received from a sample subscription to the actual targets.

Sample#

A sample subscription is one where data items are sent to the client once per sample-interval.

The minimum supported sample-interval is configurable using the field min-sample-interval, defaults to 1ms.

If within a SubscribeRequest the received sample-interval is zero, the default-sample-interval is used, defaults to 1s.

Configuration#

gnmi-server:
  # the address the gNMI server will listen to
  address: :57400
  # if true, the server will not verify the client's certificates
  skip-verify: false
  # path to the CA certificate file to be used, irrelevant if `skip-verify` is true
  ca-file: 
  # path to the server certificate file
  cert-file:
  # path to the server key file
  key-file:
  # maximum number of allowed subscriptions
  max-subscriptions: 64
  # maximum number of active Get/Set RPCs
  max-unary-rpc: 64
  # defines the minimum allowed sample interval, this value is used when the received sample-interval 
  # is greater than zero but lower than this minimum value.
  min-sample-interval: 1ms
  # defines the default sample interval, 
  # this value is used when the received sample-interval is zero within a stream/sample subscription.
  default-sample-interval: 1s
  # defines the minimum heartbeat-interval
  # this value is used when the received heartbeat-interval is greater than zero but
  # lower than this minimum value
  min-heartbeat-interval: 1s
  # enables the collection of Prometheus gRPC server metrics
  enable-metrics: false
  # enable additional debug logs
  debug: false
  # Enables Consul service registration
  service-registration:
    # Consul server address, default to localhost:8500
    address:
    # Consul Data center, defaults to dc1
    datacenter: 
    # Consul username, to be used as part of HTTP basicAuth
    username:
    # Consul password, to be used as part of HTTP basicAuth
    password:
    # Consul Token, is used to provide a per-request ACL token 
    # which overrides the agent's default token
    token:
    # gnmi server service check interval, only TTL Consul check is enabled
    # defaults to 5s
    check-interval:
    # Maximum number of failed checks before the service is deleted by Consul
    # defaults to 3
    max-fail:
    # Consul service name
    name:
    # List of tags to be added to the service registration, 
    # if available, the instance-name and cluster-name will be added as tags,
    # in the format: gnmic-instance=$instance-name and gnmic-cluster=$cluster-name
    tags:

Secure vs Insecure Server#

Insecure Mode#

By default, the server runs in insecure mode, as long as skip-verify is false and none of ca-file, cert-file and key-file are set.

Secure Mode#

To run this gNMI server in secure mode, there are a few options:

  • Using self signed certificates, without client certificate verification:
gnmi-server:
  skip-verify: true
  • Using self signed certificates, with client certificate verification:
gnmi-server:
# a valid CA certificate to verify the client provided certificates
  ca-file: /path/to/caFile 
  • Using CA provided certificates, without client certificate verification:
gnmi-server:
  skip-verify: true
  # a valid server certificate
  cert-file: /path/to/server-cert
  # a valid server key
  key-file:  /path/to/server-key
  • Using CA provided certificates, with client certificate verification:
gnmi-server:
  # a valid CA certificate to verify the client provided certificates
  ca-file: /path/to/caFile 
  # a valid server certificate
  cert-file: /path/to/server-cert
  # a valid server key
  key-file:  /path/to/server-key

Fields#

address#

Defines the address the gNMI server will listen to.

This can be a tcp socket in the format <addr:port> or a unix socket starting with unix:///

skip-verify#

If true, the server will not verify the client's certificates.

ca-file#

Defines the path to the CA certificate file to be used, irrelevant if skip-verify is true

cert-file#

Defines the path to the server certificate file to be used.

key-file#

Defines the path to the server key file to be used.

max-subscriptions#

Defines the maximum number of allowed subscriptions.

Defaults to 64.

max-unary-rpc#

Defines the maximum number of active Get/Set RPCs.

Defaults to 64.

min-sample-interval#

Defines the minimum allowed sample interval, this value is used when the received sample-interval is greater than zero but lower than this minimum value.

Defaults to 1ms

default-sample-interval#

Defines the default sample interval, this value is used when the received sample-interval is zero within a stream/sample subscription.

Defaults to 1s

min-heartbeat-interval#

Defines the minimum heartbeat-interval, this value is used when the received heartbeat-interval is greater than zero but lower than this minimum value.

Defaults to 1s

enable-metrics#

Enables the collection of Prometheus gRPC server metrics.

debug#

Enables additional debug logging.

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