Sandbox Service References

A sandbox may contain one or more forked workloads within itself. In some cases, it may be desirable to have one forked workload be configured dynamically to reference the other. This document details how this can be done using Signadot Sandboxes.

For configuring references to one fork from another, we make use of dynamic expressions. These expressions are special values that can be specified as one of the environment variables on a fork. At runtime, these values are computed and made available to the forked workloads.

Usage

CLI+yaml
Java
Python

# file: cross-forks-refs.yaml
# usage: signadot sandbox apply -f cross-fork-refs.yaml
name: cross-fork-sandbox
spec:
  cluster: ...
  forks:  # create 2 forks, "frontend" and "customer"
  - forkOf:
      kind: Deployment
      namespace: hotrod
      name: frontend
    customizations:
      images:
      - image: frontend:dev
  - forkOf:
      kind: Deployment
      namespace: hotrod
      name: customer
    customizations:
      env:
        name: FRONTEND_DEV
        valueFrom:  # set FRONTEND_DEV env var to the host:port of the forked frontend workload.
          fork:
            forkOf:
              kind: Deployment
              namespace: hotrod
              name: frontend
            expression: "{{ .Service.Host }}:{{ .Service.Port }}"

// ... imports and instantiation of the API client

SandboxFork frontendFork = new SandboxFork()
  .forkOf(new SandboxForkOf().kind("Deployment").namespace(HOTROD).name("frontend"))
  .customizations(new SandboxCustomizations()
    .addImagesItem(new SandboxImage().image(HOTROD_TEST_IMAGE))
  );

SandboxFork customerFork = new SandboxFork()
  .forkOf(new SandboxForkOf().kind("Deployment").namespace(HOTROD).name("customer"))
  .customizations(new SandboxCustomizations()
    .addImagesItem(new SandboxImage().image(HOTROD_TEST_IMAGE))
    .addEnvItem(new SandboxEnvVar().name("FROM_TEST_VAR").valueFrom(
      new SandboxEnvValueFrom().fork(
        new SandboxEnvValueFromFork().forkOf(
          new SandboxForkOf()
            .kind("Deployment")
            .namespace("hotrod")
            .name("frontend")
        ).expression("{{ .Service.Host }}:{{ .Service.Port }}")
      )
    ))
  )
  .addEndpointsItem(new SandboxForkEndpoint().name("hotrod-customer").port(8081).protocol("http"));

Sandbox request = new Sandbox()
  .spec(new SandboxSpec()
    .cluster(CLUSTER_NAME)
    .description("...")
    .addForksItem(customerFork)
    .addForksItem(frontendFork));

# ... imports and instantiation of the API client

frontend_fork = SandboxFork(
    fork_of=SandboxForkOf(
        kind="Deployment",
        name="frontend",
        namespace="hotrod"
    ),
    customizations=SandboxCustomizations(
        images=[
            SandboxImage(image=cls.HOTROD_TEST_IMAGE)
        ]
    )
)
customer_fork = SandboxFork(
    fork_of=SandboxForkOf(
        kind="Deployment",
        name="customer",
        namespace="hotrod"
    ),
    customizations=SandboxCustomizations(
        images=[
            SandboxImage(image=cls.HOTROD_TEST_IMAGE)
        ],
        env=[
            SandboxEnvVar(
                name="FROM_TEST_VAR",
                value_from=SandboxEnvValueFrom(
                    fork=SandboxEnvValueFromFork(
                        fork_of=SandboxForkOf(
                            kind="Deployment",
                            name="frontend",
                            namespace="hotrod"
                        ),
                        expression="{{ .Service.Host }}:{{ .Service.Port }}"
                    )
                )
            )
        ]
    ),
    endpoints=[
        SandboxForkEndpoint(
            name="hotrod-customer",
            port=8081,
            protocol="http"
        )
    ]
)
request = Sandbox(
    spec=SandboxSpec(
        description="...",
        cluster=cls.CLUSTER_NAME,
        forks=[customer_fork, frontend_fork]
    )
)

In the example shown above, there are two services being forked called frontend and route. We are adding a dynamic environment variable parameter to the fork of the service frontend that points dynamically to the address of the forked service called route. In this case, we can expect to find the environment variable named ROUTE_ADDR that will point to the address of the forked route service within the same sandbox at runtime. The dynamic expressions that can be used are documented below.

Template Variable	Resolves To
`{{ .Service.Host }}`	DNS host name of the specified forked workload
`{{ .Service.Port }}`	First container port of the specified forked workload

Usage​

Usage