Transports

Overview

Transport	Latency	Status
Loopback	Fastest	Available, stacked simulations (single process).
TCP	Fastest	Planned.
Redis	Faster	Recommended.
Redis PubSub	Fast	Available, stable.
RESP	Fast	Under consideration, for cloud connectivity (tunnelling).
gPPC	Fast	Under consideration, for cloud connectivity (HTTP).
Redis Async	Slower	Available, experimental.
MsgQueue	Slowest	Discontinued, poor performance at scale.

Usage

A transport can be specified in a number of ways, however typically a transport will be configured in a Stack Configuration (YAML) or via an Environment Variable.

Stack Configuration

Example Simulation Stack

simulation.yaml

---
kind: Stack
metadata:
  name: example
spec:
  connection:
    transport:
      redis:
        uri: redis://localhost:6379
        timeout: 60

Environment Variables

Variable	CLI Option (ModelC/Simer)	Default
`SIMBUS_TRANSPORT`	`--transport`	`redispubsub`
`SIMBUS_URI`	`--uri`	`redis://localhost:6379`
N/A	`--timeout`	`60` (seconds)

Note: Simer parameters have only a single - prefix (i.e. -transport). Environment variables can be specified with the -env parameter.

Transports

Loopback

@startuml transport-loopback
skinparam nodesep 55
skinparam ranksep 40
skinparam componentStyle rectangle
skinparam FrameBorderColor #c0c0c0
skinparam FrameFontColor #c0c0c0
skinparam FrameFontStyle italic

frame "Stack (single process)" {
    component "Model" as m1
    component "Model" as m2
    interface "Loopback" as SBif
    m1 -left-> SBif
    m2 -right-> SBif
}
@enduml

The loopback transport implements a limited SimBus algorithm which makes it possible to run a model, or a stack of models, without connecting to a SimBus. Because the messaging associated with connecting to a SimBus is removed (or internalised) by the loopback, this is the fastest transport available when building simulations, however it is only suitable for particular deployment scenarios and when developing models.

Note: The loopback transport is only suitable for stacked simulations (i.e. models are arranged within single process).

Configuration Parameters

Parameter	Example
`transport` (name)	`loopback`
`uri`	`loopback`
`timeout` (seconds)	`60`

Redis

@startuml transport-redis
skinparam nodesep 55
skinparam ranksep 40
skinparam componentStyle rectangle

component "Model" as m1
component "Model" as m2
component "SimBus" as sb
interface "Redis" as red
m1 -left-> red
m2 -right-> red
sb <-down-> red

@enduml

The redis transport is recommended for connecting models in a simulation. It uses blocking Redis commands and simple data types to implement a message exchange mechanism.

Configuration Parameters

Parameter	Example
`transport` (name)	`redis`
`uri`	`redis://localhost:6379`
`timeout` (seconds)	`60`

Redis Async

@startuml transport-redisasync
skinparam nodesep 55
skinparam ranksep 40
skinparam componentStyle rectangle

component "Model" as m1
component "Model" as m2
component "SimBus" as sb
interface "Redis Async" as red
m1 -left-> red
m2 -right-> red
sb <-down-> red

@enduml

An experimental transport which uses and asynchronous Redis library. The performance was slower than expected; its still fast, however the redis transport is faster; and development has stopped.

Configuration Parameters

Parameter	Example
`transport` (name)	`redis`
`uri`	`redisasync://localhost:6379`
`timeout` (seconds)	`60`

Redis PUB/SUB

@startuml transport-redispubsub
skinparam nodesep 55
skinparam ranksep 40
skinparam componentStyle rectangle

component "Model" as m1
component "Model" as m2
component "SimBus" as sb
interface "Redis PubSub" as red
m1 -left-> red
m2 -right-> red
sb <-down-> red

@enduml

The redispubsub transport is the original, and reference, implementaion. Migration to the newer redis transport is recommended.

Note: In some deployment scenarios, particularly clould environments, the redispubsub transport might not work. In such cases the newer redis transport will operate correctly.

Configuration Parameters

Parameter	Example
`transport` (name)	`redispubsub`
`uri`	`redis://localhost:6379`
`timeout` (seconds)	`60`