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Configuration management relies on orchestration technology to update managed systems. Salt orchestration is centralized by the Orchestrate Runner feature.
Salt Orchestrate Runner controls the activities of minions -- the individual IT systems that Salt manages -- from the master. Orchestrate Runner enables admins to coordinate the activities of multiple machines from a central place. It also gives Salt users an enterprise view of IT deployment architecture.
A simple example of Salt orchestration is to use the tool to install Elastic's ElasticSearch tool on 10 servers. You could send instructions to minions on all 10 machines, which is automated and saves manual work. However, you might want to first create additional loopback network interfaces so that you can run more than one instance of Elasticsearch on each machine. These commands should run in a certain order rather than all at once, which requires orchestration on top of automation. Another benefit of Salt orchestration is that Orchestrate Runner recognizes dependencies between operations on different machines, so it stops when there is a failure.
Command syntax and folder structure
Salt's commands for Orchestrate Runner are similar to those for minions, with some notable differences.
The command syntax in the Salt state files, which use the suffix .sls, is the same, except that Orchestrate Runner uses state.orchestrate and salt-run, while minion commands use salt. For Salt users who run minions without a master, try salt-call.
While there are many ways to run Salt modules and functions, administrators can get a sense of the Salt orchestration commands by comparing them with those for minions. To apply state, for example, for a state file ng, the command structure for Orchestrate Runner is:
sudo salt-run state.orchestrate orch.ng
By comparison, for minions, the command below applies state to all minions and runs all the .sls files in /srv/salt.
sudo salt '*' state.apply
The orchestration state file lives in the /srv/salt/orch folder, not /srv/salt, which is the default location for minion instructions.
A Salt orchestration example
To understand how Salt orchestration works in real IT deployments, follow this example based on deploying web server and load balancing tool Ngnix.
The user creates the .sls file /srv/salt/orch/ng.sls for Nginx configuration. The sequence either installs Nginx or verifies that it is running and then creates a second loopback IP address, 127.0.0.2. The tgt argument means to run this configuration sequence against the server named paris.
Use cmd.run, and then give the command next to name. Here, it runs ifconfig.
Salt runs the commands in the .sls file from top to bottom, with no dependency between them in this example.
- tgt: 'paris'
- pkg: nginx
- name: ifconfig lo:0 127.0.0.2 netmask 255.0.0.0 up
Run the configuration sequence sudo salt-run state.orchestrate orch.ng, and observe the output:
Comment: All specified packages are already installed
Duration: 300.927 ms
Comment: The service nginx is already running
Duration: 27.888 ms
Name: ifconfig lo:0 127.0.0.2 netmask 255.0.0.0 up
Comment: Command "ifconfig lo:0 127.0.0.2 netmask 255.0.0.0 up" run
Duration: 6.45 ms
Summary for paris_master
Succeeded: 3 (changed=1)
Total states run: 3
Total run time: 335.265 ms
Then, run ifconfig on that server. The new loopback interface is added:
lo:0 Link encap:Local Loopback
inet addr:127.0.0.2 Mask:255.0.0.0
UP LOOPBACK RUNNING MTU:65536 Metric:1
This Salt orchestration example illustrates that a single state file can include multiple commands that result in complex automated steps.
While this example did not include command dependencies, Orchestrate Runner does support them. For example, you can write Python code to raise an error if something is missing or otherwise fails in the configuration. In that case, return the error to Orchestrate Runner by putting a value in the Python object __context__['retcode']. To create dependencies between commands in a state file, use global state objects require or require_any.
Orchestrate Runner is no more complicated than minions, and it follows the same syntax for the Salt user. The only difference is that Orchestrate Runner works at the master level, which provides a central point to control more than one minion and operation simultaneously. Play with its possibilities via in-line Jinja template variables, custom execution modules and other devices.