# Salt Syndic

The most basic or typical Salt topology consists of a single Master node controlling a group of Minion nodes. An intermediate node type, called Syndic, when used offers greater structural flexibility and scalability in the construction of Salt topologies than topologies constructed only out of Master and Minion node types.

A Syndic node can be thought of as a special passthrough Minion node. A Syndic node consists of a `salt-syndic` daemon and a `salt-master` daemon running on the same system. The `salt-master` daemon running on the Syndic node controls a group of lower level Minion nodes and the `salt-syndic` daemon connects higher level Master node, sometimes called a Master of Masters.

The `salt-syndic` daemon relays publications and events between the Master node and the local `salt-master` daemon. This gives the Master node control over the Minion nodes attached to the `salt-master` daemon running on the Syndic node.

## Configuring the Syndic

To setup a Salt Syndic you need to tell the Syndic node and its Master node about each other. If your Master node is located at `10.10.0.1`, then your configurations would be:

On the Syndic node:

    # /etc/salt/master
    syndic_master: 10.10.0.1  # may be either an IP address or a hostname

    # /etc/salt/minion

    # id is shared by the salt-syndic daemon and a possible salt-minion daemon
    # on the Syndic node
    id: my_syndic

On the Master node:

    # /etc/salt/master
    order_masters: True

The `syndic_master` option tells the Syndic node where to find the Master node in the same way that the `master` option tells a Minion node where to find a Master node.

The `id` option is used by the `salt-syndic` daemon to identify with the Master node and if unset will default to the hostname or IP address of the Syndic just as with a Minion.

The `order_masters` option configures the Master node to send extra information with its publications that is needed by Syndic nodes connected directly to it.

Warning

The syndic process must be run as the same user as the syndic master.

Note

Each Syndic must provide its own `file_roots` directory. Files will not be automatically transferred from the Master node.

## Configuring the Syndic with Multimaster

Added in version 2015.5.0.

Syndic with Multimaster lets you connect a syndic to multiple masters to provide an additional layer of redundancy in a syndic configuration.

Higher level masters should first be configured in a multimaster configuration. See Multimaster Tutorial.

On the syndic, the `syndic_master` option is populated with a list of the higher level masters.

Since each syndic is connected to each master, jobs sent from any master are forwarded to minions that are connected to each syndic. If the `master_id` value is set in the master config on the higher level masters, job results are returned to the master that originated the request in a best effort fashion. Events/jobs without a `master_id` are returned to any available master.

## Running the Syndic

The `salt-syndic` daemon is a separate process that needs to be started in addition to the `salt-master` daemon running on the Syndic node. Starting the `salt-syndic` daemon is the same as starting the other Salt daemons.

The Master node in many ways sees the Syndic as an ordinary Minion node. In particular, the Master will need to accept the Syndic's Minion key as it would for any other Minion.

On the Syndic node:

    # salt-syndic
    or
    # service salt-syndic start

On the Master node:

    # salt-key -a my_syndic

The Master node will now be able to control the Minion nodes connected to the Syndic. Only the Syndic key will be listed in the Master node's key registry but this also means that key activity between the Syndic's Minions and the Syndic does not encumber the Master node. In this way, the Syndic's key on the Master node can be thought of as a placeholder for the keys of all the Minion and Syndic nodes beneath it, giving the Master node a clear, high level structural view on the Salt cluster.

On the Master node:

    # salt-key -L
    Accepted Keys:
    my_syndic
    Denied Keys:
    Unaccepted Keys:
    Rejected Keys:

    # salt '*' test.version
    minion_1:
        2018.3.4
    minion_2:
        2018.3.4
    minion_4:
        2018.3.4
    minion_3:
        2018.3.4

## Topology

A Master node (a node which is itself not a Syndic to another higher level Master node) must run a `salt-master` daemon and optionally a `salt-minion` daemon.

A Syndic node must run `salt-syndic` and `salt-master` daemons and optionally a `salt-minion` daemon.

A Minion node must run a `salt-minion` daemon.

When a `salt-master` daemon issues a command, it will be received by the Syndic and Minion nodes directly connected to it. A Minion node will process the command in the way it ordinarily would. On a Syndic node, the `salt-syndic` daemon will relay the command to the `salt-master` daemon running on the Syndic node, which then propagates the command to the Minions and Syndics connected to it.

When events and job return data are generated by `salt-minion` daemons, they are aggregated by the `salt-master` daemon they are connected to, which `salt-master` daemon then relays the data back through its `salt-syndic` daemon until the data reaches the Master or Syndic node that issued the command.

## Syndic wait

`syndic_wait` is a master configuration file setting that specifies the number of seconds the Salt client should wait for additional syndics to check in with their lists of expected minions before giving up. This value defaults to `5` seconds.

The `syndic_wait` setting is necessary because the higher-level master does not have a way of knowing which minions are below the syndics. The higher-level master has its own list of expected minions and the masters below them have their own lists as well, so the Salt client does not know how long to wait for all returns. The `syndic_wait` option allows time for all minions to return to the Salt client.

Note

To reduce the amount of time the CLI waits for Minions to respond, install a Minion on the Syndic or tune the value of the `syndic_wait` configuration.

While it is possible to run a Syndic without a Minion installed on the same system, it is recommended, for a faster CLI response time, to do so. Without a Minion installed on the Syndic node, the timeout value of `syndic_wait` increases significantly - about three-fold. With a Minion installed on the Syndic, the CLI timeout resides at the value defined in `syndic_wait`.

Note

If you have a very large infrastructure or many layers of Syndics, you may find that the CLI doesn't wait long enough for the Syndics to return their events. If you think this is the case, you can set the `syndic_wait` value in the Master configs on the Master or Syndic nodes from which commands are executed. The default value is `5`, and should work for the majority of deployments.

In order for a Master or Syndic node to return information from Minions that are below their Syndics, the CLI requires a short wait time in order to allow the Syndics to gather responses from their Minions. This value is defined in the `syndic_wait` config option and has a default of five seconds.

## Syndic config options

These are the options that can be used to configure a Syndic node. Note that other than `id`, Syndic config options are placed in the Master config on the Syndic node.

> - `id`: Syndic id (shared by the `salt-syndic` daemon with a potential `salt-minion` daemon on the same system)

> - `syndic_master`: Master node IP address or hostname

> - `syndic_master_port`: Master node ret_port

> - `syndic_log_file`: path to the logfile (absolute or not)

> - `syndic_pidfile`: path to the pidfile (absolute or not)

> - `syndic_wait`: time in seconds to wait on returns from this syndic

## Minion Data Cache

Beginning with Salt 2016.11.0, the Pluggable Minion Data Cache was introduced. The minion data cache contains the Salt Mine data, minion grains, and minion pillar information cached on the Salt Master. By default, Salt uses the `localfs` cache module, but other external data stores can be used instead.

Using a pluggable minion cache modules allows for the data stored on a Salt Master about Salt Minions to be replicated on other Salt Masters the Minion is connected to. Please see the Minion Data Cache documentation for more information and configuration examples.