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CORE Services

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.

Available Services

Service Group Services
BIRD BGP, OSPF, RADV, RIP, Static
EMANE Transport Service
FRR BABEL, BGP, OSPFv2, OSPFv3, PIMD, RIP, RIPNG, Zebra
NRL arouted, MGEN Sink, MGEN Actor, NHDP, OLSR, OLSRORG, OLSRv2, SMF
Quagga BABEL, BGP, OSPFv2, OSPFv3, OSPFv3 MDR, RIP, RIPNG, XPIMD, Zebra
SDN OVS, RYU
Security Firewall, IPsec, NAT, VPN Client, VPN Server
Utility ATD, Routing Utils, DHCP, FTP, IP Forward, PCAP, RADVD, SSF, UCARP
XORP BGP, OLSR, OSPFv2, OSPFv3, PIMSM4, PIMSM6, RIP, RIPNG, Router Manager

Node Types and Default Services

Here are the default node types and their services:

Node Type 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.

NOTE: To start, stop, and restart services during run-time, right-click a node and use the Services… menu.

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.

Leveraging UserDefined

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.

Creating New Services

  1. Modify the example service shown below to do what you want. It could generate config/script files, mount per-node directories, start processes/scripts, etc. sample.py is a Python file that defines one or more classes to be imported. You can create multiple Python files that will be imported. Add any new filenames to the init.py file.

  2. Put these files in a directory such as /home/username/.core/myservices Note that the last component of this directory name myservices should not be named something like services which conflicts with an existing Python name (the syntax ‘from myservices import *’ is used).

  3. Add a custom_services_dir = /home/username/.core/myservices entry to the /etc/core/core.conf file.

    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.

  4. Restart the CORE daemon (core-daemon). Any import errors (Python syntax) should be displayed in the /var/log/core-daemon.log log file (or on screen).

  5. Start using your custom service on your nodes. You can create a new node type that uses your service, or change the default services for an existing node type, or change individual nodes.

If you have created a new service type that may be useful to others, please consider contributing it to the CORE project.

Example Custom Service

Below is the skeleton for a custom service with some documentation. Most people would likely only setup the required class variables (name/group). Then define the configs (files they want to generate) and implement the generate_config function to dynamically create the files wanted. Finally the startup commands would be supplied, which typically tends to be running the shell files generated.

"""
Simple example custom service, used to drive shell commands on a node.
"""
from typing import Tuple

from core.nodes.base import CoreNode
from core.services.coreservices import CoreService, ServiceMode


class ExampleService(CoreService):
    """
    Example Custom CORE Service

    :cvar name: name used as a unique ID for this service and is required, no spaces
    :cvar group: allows you to group services within the GUI under a common name
    :cvar executables: executables this service depends on to function, if executable is
        not on the path, service will not be loaded
    :cvar dependencies: services that this service depends on for startup, tuple of
        service names
    :cvar dirs: directories that this service will create within a node
    :cvar configs: files that this service will generate, without a full path this file
        goes in the node's directory e.g. /tmp/pycore.12345/n1.conf/myfile
    :cvar startup: commands used to start this service, any non-zero exit code will
        cause a failure
    :cvar validate: commands used to validate that a service was started, any non-zero
        exit code will cause a failure
    :cvar validation_mode: validation mode, used to determine startup success.
        NON_BLOCKING    - runs startup commands, and validates success with validation commands
        BLOCKING        - runs startup commands, and validates success with the startup commands themselves
        TIMER           - runs startup commands, and validates success by waiting for "validation_timer" alone
    :cvar validation_timer: time in seconds for a service to wait for validation, before
        determining success in TIMER/NON_BLOCKING modes.
    :cvar validation_period: period in seconds to wait before retrying validation,
        only used in NON_BLOCKING mode
    :cvar shutdown: shutdown commands to stop this service
    """

    name: str = "ExampleService"
    group: str = "Utility"
    executables: Tuple[str, ...] = ()
    dependencies: Tuple[str, ...] = ()
    dirs: Tuple[str, ...] = ()
    configs: Tuple[str, ...] = ("myservice1.sh", "myservice2.sh")
    startup: Tuple[str, ...] = tuple(f"sh {x}" for x in configs)
    validate: Tuple[str, ...] = ()
    validation_mode: ServiceMode = ServiceMode.NON_BLOCKING
    validation_timer: int = 5
    validation_period: float = 0.5
    shutdown: Tuple[str, ...] = ()

    @classmethod
    def on_load(cls) -> None:
        """
        Provides a way to run some arbitrary logic when the service is loaded, possibly
        to help facilitate dynamic settings for the environment.

        :return: nothing
        """
        pass

    @classmethod
    def get_configs(cls, node: CoreNode) -> Tuple[str, ...]:
        """
        Provides a way to dynamically generate the config files from the node a service
        will run. Defaults to the class definition and can be left out entirely if not
        needed.

        :param node: core node that the service is being ran on
        :return: tuple of config files to create
        """
        return cls.configs

    @classmethod
    def generate_config(cls, node: CoreNode, filename: str) -> str:
        """
        Returns a string representation for a file, given the node the service is
        starting on the config filename that this information will be used for. This
        must be defined, if "configs" are defined.

        :param node: core node that the service is being ran on
        :param filename: configuration file to generate
        :return: configuration file content
        """
        cfg = "#!/bin/sh\n"
        if filename == cls.configs[0]:
            cfg += "# auto-generated by MyService (sample.py)\n"
            for iface in node.get_ifaces():
                cfg += f'echo "Node {node.name} has interface {iface.name}"\n'
        elif filename == cls.configs[1]:
            cfg += "echo hello"
        return cfg

    @classmethod
    def get_startup(cls, node: CoreNode) -> Tuple[str, ...]:
        """
        Provides a way to dynamically generate the startup commands from the node a
        service will run. Defaults to the class definition and can be left out entirely
        if not needed.

        :param node: core node that the service is being ran on
        :return: tuple of startup commands to run
        """
        return cls.startup

    @classmethod
    def get_validate(cls, node: CoreNode) -> Tuple[str, ...]:
        """
        Provides a way to dynamically generate the validate commands from the node a
        service will run. Defaults to the class definition and can be left out entirely
        if not needed.

        :param node: core node that the service is being ran on
        :return: tuple of commands to validate service startup with
        """
        return cls.validate