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123 lines
4.6 KiB
123 lines
4.6 KiB
SystemD Socket Activation for Asterisk
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======================================
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This folder contains sample unit files which can be used as the basis of a
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socket activated Asterisk deployment. Socket activation support currently
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extends to the following listeners:
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* Asterisk Command-line Interface
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* Asterisk Manager Interface (clear text and TLS)
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* Builtin HTTP / HTTPS server
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The primary use case of this feature is to allow Asterisk to be started by
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other services through use of AMI, CLI or REST API.
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The examples and documentation assume that Asterisk was linked to libsystemd
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when compiled. This integration is required for `Type=notify` and socket
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activation to work.
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Security
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========
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Care must be take if enabling socket activation on any IP:PORT that is not
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protected by a firewall. Any user that can reach any socket activation
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port can start Asterisk, even if they do not have valid credentials to sign
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into the service in question. Enabling HTTP socket activation on a system
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which provides SIP over websockets would allow remote users to start Asterisk
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any time the HTTP socket is running.
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This functionality bypasses the normal restriction where only 'root' can start
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a service. Enabling AMI socket activation allows any user on the local server
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to start Asterisk by running 'telnet localhost 5038'.
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CLI activation is secured by the combination of SocketUser, SocketGroup and
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SocketMode settings in the systemd socket. Only local users with access will
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be able to start asterisk by using CLI.
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Separate .socket units or a single unit
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=======================================
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Asterisk is a complex system with many components which can be enabled or
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disabled individually. Using socket activation requires deciding to use
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a single socket file or multiple separate socket files.
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The remainder of this README assumes separate socket units are used for each
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listener.
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Service and Socket files
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========================
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All .socket and .service examples in this folder use "reasonable" default
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paths for Linux. Depending on your distribution and ./configure options
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you may need to modify these before installing. The files are meant to
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be examples rather than files to be blindly installed.
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Installing and enabling socket units
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====================================
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Modify socket files as desired. Install them to a location where systemd
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will find them. pkg-config can be used to determine an appropriate location.
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For socket files to be managed directly by the local administrator:
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pkg-config systemd --variable systemdsystemconfdir
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For socket files to be deployed by package manager:
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pkg-config systemd --variable systemdsystemunitdir
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After installing socket files you must run 'systemctl daemon-reload' for
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systemd to read the added/modified units. After this you can enable the
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desired sockets, for example to enable AMI:
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systemctl enable asterisk-ami.socket
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Socket Selection
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================
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Asterisk configuration is unchanged by use of socket activation. When a
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component that supports socket activation starts a listener in Asterisk,
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any sockets provided by systemd are iterated. The systemd socket is used
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when the bound address configured by Asterisk is an exact match with the
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address given by the ListenStream setting in the systemd socket.
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Command-line Interface
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======================
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Symbolic links do not appear to be resolved when checking the CLI listener.
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This may be of concern since /var/run is often a symbolic link to /run. Both
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Asterisk and systemd must use /var/run, or both must use /run. Mismatching
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will result in service startup failure.
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When socket activation is used for Asterisk CLI some asterisk.conf options
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are ignored. The following options from the [files] section are ignored
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and must instead be set by the systemd socket file.
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* astctlowner - use SocketUser
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* astctlgroup - use SocketGroup
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* astctlpermissions - use SocketMode
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See asterisk-cli.socket for an example of these settings.
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Stopping Asterisk
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=================
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Some existing asterisk.service files use CLI 'core stop now' for the ExecStop
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command. It is not recommended to use CLI to stop Asterisk on systems where
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CLI socket activation is enabled. If Asterisk fails to start systemd still
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tries running the ExecStop command. This can result in an loop where ExecStop
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causes CLI socket activation to start Asterisk again. A better way to deal
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with shutdown is to use Type=notify and do not specify an ExecStop command.
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See the example asterisk.service.
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Unused Sockets
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==============
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Asterisk makes no attempt to check for sockets provided by systemd that are not
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used. It is the users responsibility to only provide sockets which Asterisk is
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configured to use.
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