ClInit

A lightweight and simple to use cluster management tool.

A name was derived from "cluster init". But you can read that as "cloud init" because everything is in clouds nowadays.

What it is

It is a cluster management tool:

• runs start, stop and other management commands you used to see in init scripts;
• runs commands on a group of hosts simultaneously using ssh and honoring dependencies;
• shows you service status, visualize dependency tree for you and helps you with clusters

What it is not

• Not a clustering tool: won't detect node failure for you
• Not a deployment tool. While it is possible to install software with clinit, it is not intended usage

Example usage

~]$ clinit grouplist
all
hadoop
hbase
impala
zookeeper-server
~]$ clinit status impala
hat0:impala-catalog is started
hat0:impala-state-store is started
hat1:impala-server is started
hat2:impala-server is started
hat3:impala-server is started
~]$ clinit tree impala
hat0:impala-catalog─┬─hat0:hive-metastore───hat0:mysql-meta
└─hat0:impala-state-store
hat2:impala-server─┬─hat0:hdfs-namenode
└─hat0:impala-state-store
hat3:impala-server─┬─hat0:hdfs-namenode
└─hat0:impala-state-store

Configuration

Default configuration is read from /etc/clinit/services.xml . As you might guess, it's a generic XML file.

 <?xml version="1.0" encoding="utf-8"?>
<servicesxmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"effective_user="root"effective_group="root"ssh_key="/root/.ssh/id_rsa">
<serviceid="mariadb"host="localhost"start="service mariadb start"stop="service mariadb stop"status="service mariadb status">
</service>
<serviceid="httpd"host="localhost"start="service httpd start"stop="service httpd stop"status="service httpd status">
<requiresid="mariadb"host="localhost"strong="true"/>
</service>
<groupname="httpd">
<serviceid="httpd"host="localhost"/>
</group>
<groupname="mariadb">
<serviceid="mariadb"host="localhost"/>
</group>
</services>

• services — configuration root tag.
  • effective_user, effective_group — optional attributes. Configures a local user to use for a 'priviledged' command.
    Implementation uses sudo -u $user, so sudo should be installed and configured as required.
    See Command Invocation below for additional details. If attributes are omitted — current user and group are used;
  • ssh_key — optional attribute. If defined, ssh is used with -i $ssh_key option.
    Systems ssh client is used, so ssh configuration is honoured, ssh-agent may be used for auth.
• service — describes a single service. Usually it's a single init script;
  • attributes:
    • id — obligatory. The display and internal name of a service;
    • host — obligatory. A host which runs the service. Should be ssh accessible;
    • start, stop, status — corresponding commands. Any of these may be omitted. See Command Invocation below;
  • subtags:
    • requires — lists a required service. Can be repeated as needed.
      To be precise: requires is a tag to establish start-stop order. See Command Invocation below;
      • id attribute — obligatory, contains service tag id attribute;
      • host attribute — obligatory, contains required service tag host attribute;
      • strong attribute — if false or 0 then required service will be attempted to start, but on a fail start sequence will continue. By default it is set to 'true', so dependencies are obligatory.
• group — describes arbitary service grouping. Used for group commads.
  • service — obligatory subtag. May be repeated several times if needed.
    • id — corresponding service tag id attribute
    • host — corresponding servicetaghost` attribute

Command invocation

All command-line arguments my come in any order.

clinit [command] [options] [selectors]

Commands

Commands are hardcoded. A command marked with * is priviledged. It will have sudo -u $effective_user issued before the command if the effective_user is configured. Following commands possible:

• start * — starts selected services;
• stop * — stops selected serivces;
• status * — queries for selected services status;
• restart * — stops and then starts selected services;
• condrestart * — stops and then starts only serives it previously stopped;
• list, ls — display list of services in the configuration;
• grouplist, gl — dislay list of groups in the configuration;
• keyscan — outputs the result of ssh-keyscan for selected hosts;
• tree — displays services dependency tree

Default behaviour

This behaviour can be configured with command line options. See below.
Each time a command is invoked a dependency tree is built and then each service is queried for the status. If a service lacks status command - it will be invoked directly, without status queries. If a service is running it's dependencies are not checked
If status is not matched - an action is invoked. If there is no corresponding action (start or stop) then the service is silently skipped.

You may use the latter property to build a pre-start, pre-stop, post-start, post-stop scripts. For example, you may checkout service configuration or run a configuration management utility.

Selectors

Anything which is not a command or an option and is not started with - sign is treated as a selector.

Selectors are:

• built-in all keyword. This is the default selector if none is used
• a host name;
• a service name;
• a group name;
• A colon separated host:id pair, possibly with either part omitted;
• a glob pattern of the above entity with * or ? replacing any part except for a : sign in a pair.

If a host or id is omitted from a pair, missing part is treated as a * sign.
all keyword is used for all group or all services in a configuration if there is no all group.
Any selector may have - (minus sign) suffix to indicate negative selector. Or a + sign which is implied. A good example would be:

clinit stop all slave-

Which should stop everything except for the slave group, which will be kept in the state it is. If a service inside slave group depends on any other outside of the group — it will still be stopped too by dependency, unless --selected-deps is stated

Options

All options require a command to be specified except for --help.

• -S, --services=services.xml — change loaded services descriptor file (default is services.xml);

• -j, --jobs=N — specifies the number of jobs (commands) to run simultaneously. Use -j0 to disable jobs. Default value -j8;

• --no-deps, --nodeps — start only services selected by selectors, don't figure out dependencies;

• --force-deps — check each service dependencies even if it is running;

• --selected-deps — resolve dependencies in bounds of selected services. Command(s) will affect ONLY selected services.
  While dependencies determines services start/stop order. This switch is useful to gracefully stop or start services on specified host. Complete ignoring dependencies (--no-deps) may cause startup errors.

• --no-remote=HOST — Execute commands for specified host(s) locally.
  To disable remote execution on several hosts it is possible to use option multiple times or specify comma or space separated list: --no-remote=localhost --no-remote="local,127.0.0.1 myhost"

• -p, --probe-count=N — sets probe count to N before probe procedure considered to be failed. Defaults to 10. --probe-count=0 disables probing procedure in which case action is considerd to be successful always.

• --probe-delay=N — sets delay to N seconds between probe attempts. Default 3 sec.

• -n, --dry-run — do not execute commands

• -l, --long-list — print more information for list commands

• --no-colors, --nocolors — disable colors in output.

• -v, --verbose (incremental) — print verbose messages about running commands and other debugging information.

• -q, --quiet — suppress all informational messages from startup system. Doesn't affect list and tree commands.

• -h, --help — print brief help message and exit.

Environment

CLINIT_CONFIG environment variable can be used to override the location of the default configuration file

See also

See also example