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CORE Services
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Services
CORE uses the concept of services to specify what processes or scripts run on a node when it is started. Layer-3 nodes such as routers and PCs are defined by the services that they run.
Services may be customized for each node, or new custom services can be created. New node types can be created each having a different name, icon, and set of default services. Each service defines the per-node directories, configuration files, startup index, starting commands, validation commands, shutdown commands, and meta-data associated with a node.
NOTE: Network namespace nodes do not undergo the normal Linux boot process using the init, upstart, or systemd frameworks. These lightweight nodes use configured CORE services.
Default Services and Node Types
Here are the default node types and their services:
- router - zebra, OSFPv2, OSPFv3, and IPForward services for IGP link-state routing.
- host - DefaultRoute and SSH services, representing an SSH server having a default route when connected directly to a router.
- PC - DefaultRoute service for having a default route when connected directly to a router.
- mdr - zebra, OSPFv3MDR, and IPForward services for wireless-optimized MANET Designated Router routing.
- prouter - a physical router, having the same default services as the router node type; for incorporating Linux testbed machines into an emulation.
Configuration files can be automatically generated by each service. For example, CORE automatically generates routing protocol configuration for the router nodes in order to simplify the creation of virtual networks.
To change the services associated with a node, double-click on the node to invoke its configuration dialog and click on the Services... button, or right-click a node a choose Services... from the menu. Services are enabled or disabled by clicking on their names. The button next to each service name allows you to customize all aspects of this service for this node. For example, special route redistribution commands could be inserted in to the Quagga routing configuration associated with the zebra service.
To change the default services associated with a node type, use the Node Types dialog available from the Edit button at the end of the Layer-3 nodes toolbar, or choose Node types... from the Session menu. Note that any new services selected are not applied to existing nodes if the nodes have been customized.
The node types are saved in a ~/.core/nodes.conf file, not with the .imn file. Keep this in mind when changing the default services for existing node types; it may be better to simply create a new node type. It is recommended that you do not change the default built-in node types. The nodes.conf file can be copied between CORE machines to save your custom types.
Customizing a Service
A service can be fully customized for a particular node. From the node's configuration dialog, click on the button next to the service name to invoke the service customization dialog for that service. The dialog has three tabs for configuring the different aspects of the service: files, directories, and startup/shutdown.
NOTE: A yellow customize icon next to a service indicates that service requires customization (e.g. the Firewall service). A green customize icon indicates that a custom configuration exists. Click the Defaults button when customizing a service to remove any customizations.
The Files tab is used to display or edit the configuration files or scripts that are used for this service. Files can be selected from a drop-down list, and their contents are displayed in a text entry below. The file contents are generated by the CORE daemon based on the network topology that exists at the time the customization dialog is invoked.
The Directories tab shows the per-node directories for this service. For the default types, CORE nodes share the same filesystem tree, except for these per-node directories that are defined by the services. For example, the /var/run/quagga directory needs to be unique for each node running the Zebra service, because Quagga running on each node needs to write separate PID files to that directory.
NOTE: The /var/log and /var/run directories are mounted uniquely per-node by default. Per-node mount targets can be found in /tmp/pycore.nnnnn/nN.conf/ (where nnnnn is the session number and N is the node number.)
The Startup/shutdown tab lists commands that are used to start and stop this
service. The startup index allows configuring when this service starts relative
to the other services enabled for this node; a service with a lower startup
index value is started before those with higher values. Because shell scripts
generated by the Files tab will not have execute permissions set, the startup
commands should include the shell name, with
something like sh script.sh.
Shutdown commands optionally terminate the process(es) associated with this service. Generally they send a kill signal to the running process using the kill or killall commands. If the service does not terminate the running processes using a shutdown command, the processes will be killed when the vnoded daemon is terminated (with kill -9) and the namespace destroyed. It is a good practice to specify shutdown commands, which will allow for proper process termination, and for run-time control of stopping and restarting services.
Validate commands are executed following the startup commands. A validate command can execute a process or script that should return zero if the service has started successfully, and have a non-zero return value for services that have had a problem starting. For example, the pidof command will check if a process is running and return zero when found. When a validate command produces a non-zero return value, an exception is generated, which will cause an error to be displayed in the Check Emulation Light.
TIP: To start, stop, and restart services during run-time, right-click a node and use the Services... menu.
Creating new Services
Services can save time required to configure nodes, especially if a number of nodes require similar configuration procedures. New services can be introduced to automate tasks.
The easiest way to capture the configuration of a new process into a service is by using the UserDefined service. This is a blank service where any aspect may be customized. The UserDefined service is convenient for testing ideas for a service before adding a new service type.
To introduce new service types, a myservices/ directory exists in the user's CORE configuration directory, at ~/.core/myservices/. A detailed README.txt file exists in that directory to outline the steps necessary for adding a new service. First, you need to create a small Python file that defines the service; then the custom_services_dir entry must be set in the /etc/core/core.conf configuration file. A sample is provided in the myservices/ directory.
NOTE: The directory name used in custom_services_dir should be unique and should not correspond to any existing Python module name. For example, don't use the name subprocess or services.
If you have created a new service type that may be useful to others, please consider contributing it to the CORE project.
Here is an example service with documentation describing functionality: Example Service