Extending FSM

How to extend FSM service mesh without re-compiling it

Extending FSM with Plugin Interface

In the latest 1.3.0 version of Flomesh service mesh FSM, we have introduced a significant feature: Plugin. This feature aims to provide developers with a way to extend the functionality of the service mesh without changing the FSM itself.

Nowadays, service mesh seems to be developing in two directions. One is like Istio, which provides a lot of ready-to-use functions and is very rich in features. The other like Linkerd, Flomesh FSM, and others that uphold the principle of simplicity and provide a minimum functional set that meets the user’s needs. There is no superiority or inferiority between the two: the former is rich in features but inevitably has the additional overhead of proxy, not only in resource consumption but also in the cost of learning and maintenance; the latter is easy to learn and use, consumes fewer resources, but the provided functions might not be enough for the immediate need of user desired functionality.

It is not difficult to imagine that the ideal solution is the low cost of the minimum functional set + the flexibility of scalability. The core of the service mesh is in the data plane, and the flexibility of scalability requires a high demand for the physique of the sidecar proxy. This is also why the Flomesh service mesh chose programmable proxy Pipy as the sidecar proxy.

Pipy is a programmable network proxy for cloud, edge, and IoT. It is flexible, fast, small, programmable, and open-source. The modular design of Pipy provides a large number of reusable filters that can be assembled into pipelines to process network data. Pipy provides a set of api and small usable filters to achieve business objectives while hiding the underlying details. Additionally, Pipy scripts (programming code that implements functional logic) can be dynamically delivered to Pipy instances over the network, enabling the proxy to be extended with new features without the need for compilation or restart.

Flomesh FSM extension solution

FSM provides three new CRDs for extensibility:

  • Plugin: The plugin contains the code logic for the new functionality. The default functions provided by FSM are also available as plugins, but not in the form of a Plugin resource. These plugins can be adjusted through the Helm values file when installing FSM. For more information, refer to the built-in plugin list in the Helm values.yaml file.
  • PluginChain: The plugin chain is the execution of plugins in sequence. The system provides four plugin chains: inbound-tcp, inbound-http, outbound-tcp, outbound-http. They correspond to the OSI layer-4 and layer-7 processing stages of inbound and outbound traffic, respectively.
  • PluginConfig: The plugin configuration provides the configuration required for the plugin logic to run, which will be sent to the FSM sidecar proxy in JSON format.

For detailed information on plugin CRDs, refer to the Plugin API document.

Built-in variables

Below is a list of built-in PipyJS variables which can be imported into your custom plugins via PipyJS import keyword.

variabletypenamespacesuited for Chainsdescription
__protocolstringinboundinbound-http / inbound-tcpconnection protocol indicator
__portjsoninboundinbound-http / inbound-tcpport of inbound endpoint
__isHTTP2booleaninboundinbound-httpwhether protocol is HTTP/2
__isIngressbooleaninboundinbound-httpIngress mode enabled
__targetstringinbound/connect-tcpinbound-http / inbound-tcpDestination upstream
__pluginsjsoninboundinbound-http / inbound-tcpJSON object of inbound plugins
__servicejsoninbound-http-routinginbound-httphttp service json object
__routejsoninbound-http-routinginbound-httphttp route json object
target cluster json object
__protocolstringoutboundoutbound-http / outbound-tcpoutbound connection protocol
__portjsonoutboundoutbound-http / outbound-tcpoutbound port json object
__isHTTP2booleanoutboundoutbound-httpwhether protocol is HTTP/2
__isEgressbooleanoutboundoutbound-tcpEgress mode
__targetstringoutbound/outbound-http / outbound-tcpUpstream target
__pluginsjsonoutboundoutbound-http / outbound-tcpoutbound plugin json object
__servicejsonoutbound-http-routingoutbound-httphttp service json object
__routejsonoutbound-http-routingoutbound-httphttp route json object
target cluster json object


For a simple demonstration of how to extend FSM via Plugins, refer to below demo:


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Last modified April 11, 2024: update versions of fsm and pipy (cea5b3e)