Organizing components
<<../../../_common/components/_organizing_intro.md>>
<<../../../_common/components/_organizing_types.md>>
<<../../../_common/components/_organizing_identifying.md>>
<<../../../_common/components/_organizing_lifecycle.md>>
Exercise: Integrate components
In order for a component to be invoked, it must be present in the active
component topology. For this exercise, you will add your component to the
ffx-laboratory — a restricted collection used for development inside the
product's core realm. Collections enable components to be dynamically
created and destroyed at runtime.
<<../_common/_start_femu_with_packages.md>>
Add to the component topology
Create a new instance of the echo component using the following command:
ffx component create /core/ffx-laboratory:echo \
fuchsia-pkg://fuchsiasamples.com/echo-example#meta/echo.cm
This command accepts two parameters:
/core/ffx-laboratory:echo: This is the component moniker, representing the path inside the component topology for the component instance.fuchsia-pkg://fuchsiasamples.com/echo-example#meta/echo.cm: This is the component URL, indicating how Fuchsia should resolve the component from the package server.
A new component instance named echo now exists in the topology. Show the
details of the new instance using the following command:
You should see the following output:
```none {:.devsite-disable-click-to-copy} Moniker: /core/ffx-laboratory:echo URL: fuchsia-pkg://fuchsiasamples.com/echo-example#meta/echo.cm Type: CML dynamic component Component State: Unresolved Execution State: Stopped
Notice that the instance has been created, but the component URL has not been
resolved. Resolution happens when the framework attempts to start the instance.
### Start the component instance
Start the new `echo` component instance using the following command:
```posix-terminal
ffx component start /core/ffx-laboratory:echo
This command accepts one parameter:
/core/ffx-laboratory:echo: This is the component moniker, representing the path inside the component topology for the component instance.
This causes the component instance to start, print a greeting to the log, then exit. Open a new terminal window and filter the device logs for messages from the example:
You should see the following output in the device logs:
```none {:.devsite-disable-click-to-copy} [ffx-laboratory:echo][I] Hello, Alice, Bob, Spot!
### Explore the instance
Show the details of the `echo` instance again using the following command:
```posix-terminal
ffx component show echo
You should now see the following output:
```none {:.devsite-disable-click-to-copy} Moniker: /core/ffx-laboratory:echo URL: fuchsia-pkg://fuchsiasamples.com/echo-example#meta/echo.cm Type: CML dynamic component Component State: Resolved Incoming Capabilities: fuchsia.logger.LogSink pkg Execution State: Stopped
The component state has changed to `Resolved` and you can see more details
about the component's capabilities.
Components have no ambient capabilities to access other parts of the system.
Every capability a component requires must be explicitly routed to it through
the component topology or provided by its environment.
The `echo` component requires the `fuchsia.logger.LogSink` capability to
write to the system log. You were able to successfully view the log output
because this capability is **offered** to components in the `ffx-laboratory`
collection from the `core` realm:
```json5 {:.devsite-disable-click-to-copy}
{
collections: [
{
name: "ffx-laboratory",
},
],
offer: [
{
protocol: [ "fuchsia.logger.LogSink" ],
from: "parent",
to: "#ffx-laboratory",
},
],
}
Destroy the instance
Clean up the echo instance using the following command: