Frequently Asked Questions#


General#

What is the vpp-agent?#

A control plane agent for a VPP data plane that resides inside a single container. It comes with various plugins (e.g. ACL) for programming specific data plane functions. It is an entity completely separate from VPP. Customized or out-of-the-box VPP-based containerized VNFs can incorporate the vpp-agent.

What is cn-infra?#

Framework of libraries and plugins for building control plane agents for CNFs and applications.

Is Ligato an application?#

No. Select Ligato components (i.e. vpp-agent, prometheus plugin, etcd connectors, etc.) are used as building blocks for CNF and/or cloud-native application implementations.

They compliment each other. Both provide plugins for developers to use in implementing CNFs. For example, a VPP-based CNF will use vpp-agent plugins for data plane programmability and cn-infra plugins (e.g. etcd connector, REST, gRPC, etc.) for communications with external applications.

What is a CNF?#

Cloud Native Network Function. Containerized network functions (e.g. IPsec) subscribing to cloud-native architectural and operational principles (e.g. Kubernetes lifecycle).

What is VPP?#

Vector Packet Processing is a software platform for forwarding packets. FD.io is the open source project for VPP.

Is VPP part of Ligato?#

No. Ligato includes the vpp-agent along with other plugins providing overall management, control and lifecycle support for VPP-based CNFs and cloud-native applications.

Can Ligato be used to build non-VPP cloud-native apps?#

Yes. One example is an experimental BGP agent that does not use VPP.

Is Ligato a CNCF project?#

No. However it is a member of the larger CNCF ecosystem. Many of its plugins are based on CNCF projects (e.g. gRPC, etcd, prometheus).

Are their solutions using Ligato?#

Yes. Contiv-VPP and Network Service Mesh (NSM) use Ligato components.


Details#

What is a plugin?#

Small chunk of code performing a specific function. Ligato (vpp-agent and cn-infra) come with multiple out-of-the-box plugins. New plugins can be developed performing additional functions. Developers need only use the plugins required for their application.

How does a Ligato-built CNF talk to external apps?#

Ligato provides plugins and developers can craft their own for communicating with external applications.

What is a Key Value (KV) Data Store?#

Data store (or database) of key-value (KV) pairs. Ligato supports the commonly used/deployed KV data store solutions. Plugins can be created to interface to other external KV data stores.

What programming language does Ligato use?#

Go Programming Language developed by Google. Other cloud-native projects including Kubernetes and etcd use Go. Advantages over other languages (i.e. python, java) used in distributed systems include speed (it is a compiled language), concurrency and simplicity. External applications interfacing to a Ligato application can use any programming language.

What is protobufs?#

Protocol Buffers is a language/platform-nuetral method that defines the structure and serialized format of the data associated with the object. Here is an example of a VPP route in protobuf (.proto) format.

What is a resync?#

A vpp-agent process that maintains consistency between configuration data provided from an external source, internal vpp-agent state and the actual VPP data plane state.

What is a model?#

Each object is defined by a model consisting of a module, version and type fields.

What is the microservice label?#

A unique value assigned to a group of vpp-agents watching the KV data store for config changes with a common key prefix. This is useful if you have CNFs with different config data contained in a KV data store. More details and an example are shown here.

What does northbound (NB) mean? Same for southbound (SB)?#

NB means configuration data originates from an external source such as a KV data store. SB means configuration data present in the VPP data plane.


Using Ligato#

How do I get started?#

Start with the Quickstart Guide to quickly build and program a VPP-based CNF.

Are there any tutorials I could follow?#

Yes. See tutorials beginning with coding up a “Hello World” plugin.

Are there any example apps I could look at?#

Yes. See the examples section

Is there a CLI?#

Yes. AgentCtl supplies the developer or operator with numerous CLI commands for working with Ligato.

Can I use other CLIs?#

Absolutely. Kubernetes Kubectl and Contiv-VPP contiv-netctl are examples associated with complete Kubnetes cluster environments.

etcdctl and vppctl provide CLI commands for interacting with an etcd data store and VPP respectively. The quickstart guide contains samples for etcdctl and vppctl. The VPP CLI supported by agentctl, REST or by attaching to VPP is explained here.

How do I determine what Ligato version I am working with? Same for VPP.#

AgentCtl provides a command to display Ligato agent and VPP version information. You can also attach to the VPP CLI and run the show version command.

How is a Ligato-based application configured?#

Ligato employs a stateless configuration approach. vpp-agents “listen” for config updates stored as key-value pairs in a KV data store. There is an example from the quick start guide showing config data in etcd pushed to the vpp-agent. Ligato applications can be developed using a myriad of other configuration techniques including kubectl, Helm charts, yaml files, gRPC, REST, agentctl and so on. Here is an example using gRPC to convey config data to a vpp-agent.

What is a .conf file#

Contain plugin configuration values. Most but not all plugins have their own .conf file.


KVScheduler#

What is the KVScheduler (KVS)?#

Provides transaction-based configuration processing employing a generic (abstraction) mechanism for dependency resolution between different configuration items. For example, the KVS sorts out and resolves dependencies where an interface must be configured first before proceeding with a bridge-domain. More details on the KVS can be found here.

What is a Descriptor?#

A construct used by the KVS that describes a particular configuration object (e.g. VPP route). Among other values, descriptors define dependencies and supported create, read, update and delete (CRUD) operations. More on descriptors here.

What is a KVS Transaction?#

This is the series of configuration actions as determine by the KVS. There is a KVS transaction log function illustrating the details of a transaction.

KVS Troubleshooting#

Troubleshooting KVS operations including several tools to assist can be found here


APIs#

What RPCs are supported by Ligato?#

gRPC and REST.

What REST APIs are supported?#

VPP REST APIs are documented here. There are also REST APIs for determining the descriptors registered with the KVS and for retrieving data for visualizing the KVS graph

Can I develop my own set of customized APIs?#

Yes. The REST Handler tutorial shows you how to create a REST API for the Hello World plugin.


Where can I find support for Ligato?#

Ligato is open source software so support, issues, questions, bugs, fixes, commits, PRs and so on should be communicated and shared with the community.

Github Issues URLs:

Before opening an issue, collect as much data as possible, including:

  • VPP-Agent version/commit ID
  • VPP version/commit ID
  • VPP-Agent logs (best with debug enabled)
  • KVDB store dump if possible
  • Description of what was tried to achieve

This will help the community to quickly pinpoint and fix the problem.

Further discussions with the Ligato community can take place in the Ligato Slack Room