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mgmt

mgmt by James

Available from:

https://github.com/purpleidea/mgmt/

This documentation is available in: Markdown or PDF format.

Table of Contents

  1. Overview
  2. Project description - What the project does
  3. Setup - Getting started with mgmt
  4. Features - All things mgmt can do
  5. Resources - All built-in primitives
  6. Usage/FAQ - Notes on usage and frequently asked questions
  7. Reference - Detailed reference
  8. Examples - Example configurations
  9. Development - Background on module development and reporting bugs
  10. Authors - Authors and contact information

Overview

The mgmt tool is a next generation config management prototype. It's not yet ready for production, but we hope to get there soon. Get involved today!

Project Description

The mgmt tool is a distributed, event driven, config management tool, that supports parallel execution, and librarification to be used as the management foundation in and for, new and existing software.

For more information, you may like to read some blog posts from the author:

There is also an introductory video available. Older videos and other material is available.

Setup

During this prototype phase, the tool can be run out of the source directory. You'll probably want to use ./run.sh run --yaml examples/graph1.yaml to get started. Beware that this can cause data loss. Understand what you're doing first, or perform these actions in a virtual environment such as the one provided by Oh-My-Vagrant.

Features

This section details the numerous features of mgmt and some caveats you might need to be aware of.

Autoedges

Automatic edges, or AutoEdges, is the mechanism in mgmt by which it will automatically create dependencies for you between resources. For example, since mgmt can discover which files are installed by a package it will automatically ensure that any file resource you declare that matches a file installed by your package resource will only be processed after the package is installed.

Controlling autoedges

Though autoedges is likely to be very helpful and avoid you having to declare all dependencies explicitly, there are cases where this behaviour is undesirable.

Some distributions allow package installations to automatically start the service they ship. This can be problematic in the case of packages like MySQL as there are configuration options that need to be set before MySQL is ever started for the first time (or you'll need to wipe the data directory). In order to handle this situation you can disable autoedges per resource and explicitly declare that you want my.cnf to be written to disk before the installation of the mysql-server package.

You can disable autoedges for a resource by setting the autoedge key on the meta attributes of that resource to false.

Blog post

You can read the introductory blog post about this topic here: https://ttboj.wordpress.com/2016/03/14/automatic-edges-in-mgmt/

Autogrouping

Automatic grouping or AutoGroup is the mechanism in mgmt by which it will automatically group multiple resource vertices into a single one. This is particularly useful for grouping multiple package resources into a single resource, since the multiple installations can happen together in a single transaction, which saves a lot of time because package resources typically have a large fixed cost to running (downloading and verifying the package repo) and if they are grouped they share this fixed cost. This grouping feature can be used for other use cases too.

You can disable autogrouping for a resource by setting the autogroup key on the meta attributes of that resource to false.

Blog post

You can read the introductory blog post about this topic here: https://ttboj.wordpress.com/2016/03/30/automatic-grouping-in-mgmt/

Automatic clustering

Automatic clustering is a feature by which mgmt automatically builds, scales, and manages the embedded etcd cluster which is compiled into mgmt itself. It is quite helpful for rapidly bootstrapping clusters and avoiding the extra work to setup etcd.

If you prefer to avoid this feature. you can always opt to use an existing etcd cluster that is managed separately from mgmt by pointing your mgmt agents at it with the --seeds variable.

Blog post

You can read the introductory blog post about this topic here: https://ttboj.wordpress.com/2016/06/20/automatic-clustering-in-mgmt/

Remote ("agent-less") mode

Remote mode is a special mode that lets you kick off mgmt runs on one or more remote machines which are only accessible via SSH. In this mode the initiating host connects over SSH, copies over the mgmt binary, opens an SSH tunnel, and runs the remote program while simultaneously passing the etcd traffic back through the tunnel so that the initiators etcd cluster can be used to exchange resource data.

The interesting benefit of this architecture is that multiple hosts which can't connect directly use the initiator to pass the important traffic through to each other. Once the cluster has converged all the remote programs can shutdown leaving no residual agent.

This mode can also be useful for bootstrapping a new host where you'd like to have the service run continuously and as part of an mgmt cluster normally.

In particular, when combined with the --converged-timeout parameter, the entire set of running mgmt agents will need to all simultaneously converge for the group to exit. This is particularly useful for bootstrapping new clusters which need to exchange information that is only available at run time.

Blog post

You can read the introductory blog post about this topic here: https://ttboj.wordpress.com/2016/10/07/remote-execution-in-mgmt/

Puppet support

You can supply a Puppet manifest instead of creating the (YAML) graph manually. Puppet must be installed and in mgmt's search path. You also need the ffrank-mgmtgraph Puppet module.

Invoke mgmt with the --puppet switch, which supports 3 variants:

  1. Request the configuration from the Puppet Master (like puppet agent does)

     mgmt run --puppet agent
    
  2. Compile a local manifest file (like puppet apply)

     mgmt run --puppet /path/to/my/manifest.pp
    
  3. Compile an ad hoc manifest from the commandline (like puppet apply -e)

     mgmt run --puppet 'file { "/etc/ntp.conf": ensure => file }'
    

For more details and caveats see Puppet.md.

Blog post

An introductory post on the Puppet support is on Felix's blog.

Resources

This section lists all the built-in resources and their properties. The resource primitives in mgmt are typically more powerful than resources in other configuration management systems because they can be event based which lets them respond in real-time to converge to the desired state. This property allows you to build more complex resources that you probably hadn't considered in the past.

In addition to the resource specific properties, there are resource properties (otherwise known as parameters) which can apply to every resource. These are called meta parameters and are listed separately. Certain meta parameters aren't very useful when combined with certain resources, but in general, it should be fairly obvious, such as when combining the noop meta parameter with the Noop resource.

  • Augeas: Manipulate files using augeas.
  • Exec: Execute shell commands on the system.
  • File: Manage files and directories.
  • Hostname: Manages the hostname on the system.
  • Msg: Send log messages.
  • Noop: A simple resource that does nothing.
  • Nspawn: Manage systemd-machined nspawn containers.
  • Password: Create random password strings.
  • Pkg: Manage system packages with PackageKit.
  • Svc: Manage system systemd services.
  • Timer: Manage system systemd services.
  • Virt: Manage virtual machines with libvirt.

Augeas

The augeas resource uses augeas commands to manipulate files.

Exec

The exec resource can execute commands on your system.

File

The file resource manages files and directories. In mgmt, directories are identified by a trailing slash in their path name. File have no such slash.

Path

The path property specifies the file or directory that we are managing.

Content

The content property is a string that specifies the desired file contents.

Source

The source property points to a source file or directory path that we wish to copy over and use as the desired contents for our resource.

State

The state property describes the action we'd like to apply for the resource. The possible values are: exists and absent.

Recurse

The recurse property limits whether file resource operations should recurse into and monitor directory contents with a depth greater than one.

Force

The force property is required if we want the file resource to be able to change a file into a directory or vice-versa. If such a change is needed, but the force property is not set to true, then this file resource will error.

Hostname

The hostname resource manages static, transient/dynamic and pretty hostnames on the system and watches them for changes.

static_hostname

The static hostname is the one configured in /etc/hostname or a similar file. It is chosen by the local user. It is not always in sync with the current host name as returned by the gethostname() system call.

transient_hostname

The transient / dynamic hostname is the one configured via the kernel's sethostbyname(). It can be different from the static hostname in case DHCP or mDNS have been configured to change the name based on network information.

pretty_hostname

The pretty hostname is a free-form UTF8 host name for presentation to the user.

hostname

Hostname is the fallback value for all 3 fields above, if only hostname is specified, it will set all 3 fields to this value.

Msg

The msg resource sends messages to the main log, or an external service such as systemd's journal.

Noop

The noop resource does absolutely nothing. It does have some utility in testing mgmt and also as a placeholder in the resource graph.

Nspawn

The nspawn resource is used to manage systemd-machined style containers.

Password

The password resource can generate a random string to be used as a password. It will re-generate the password if it receives a refresh notification.

Pkg

The pkg resource is used to manage system packages. This resource works on many different distributions because it uses the underlying packagekit facility which supports different backends for different environments. This ensures that we have great Debian (deb/dpkg) and Fedora (rpm/dnf) support simultaneously.

Svc

The service resource is still very WIP. Please help us my improving it!

Timer

This resource needs better documentation. Please help us my improving it!

Virt

The virt resource can manage virtual machines via libvirt.

Usage and frequently asked questions

(Send your questions as a patch to this FAQ! I'll review it, merge it, and respond by commit with the answer.)

Why did you start this project?

I wanted a next generation config management solution that didn't have all of the design flaws or limitations that the current generation of tools do, and no tool existed!

Why did you use etcd? What about consul?

Etcd and consul are both written in golang, which made them the top two contenders for my prototype. Ultimately a choice had to be made, and etcd was chosen, but it was also somewhat arbitrary. If there is available interest, good reasoning, and patches, then we would consider either switching or supporting both, but this is not a high priority at this time.

Can I use an existing etcd cluster instead of the automatic embedded servers?

Yes, it's possible to use an existing etcd cluster instead of the automatic, elastic embedded etcd servers. To do so, simply point to the cluster with the --seeds variable, the same way you would if you were seeding a new member to an existing mgmt cluster.

The downside to this approach is that you won't benefit from the automatic elastic nature of the embedded etcd servers, and that you're responsible if you accidentally break your etcd cluster, or if you use an unsupported version.

What does the error message about an inconsistent dataDir mean?

If you get an error message similar to:

Etcd: Connect: CtxError...
Etcd: CtxError: Reason: CtxDelayErr(5s): No endpoints available yet!
Etcd: Connect: Endpoints: []
Etcd: The dataDir (/var/lib/mgmt/etcd) might be inconsistent or corrupt.

This happens when there are a series of fatal connect errors in a row. This can happen when you start mgmt using a dataDir that doesn't correspond to the current cluster view. As a result, the embedded etcd server never finishes starting up, and as a result, a default endpoint never gets added. The solution is to either reconcile the mistake, and if there is no important data saved, you can remove the etcd dataDir. This is typically /var/lib/mgmt/etcd/member/.

Why do resources have both a Compare method and an IFF (on the UID) method?

The Compare() methods are for determining if two resources are effectively the same, which is used to make graph change delta's efficient. This is when we want to change from the current running graph to a new graph, but preserve the common vertices. Since we want to make this process efficient, we only update the parts that are different, and leave everything else alone. This Compare() method can tell us if two resources are the same.

The IFF() method is part of the whole UID system, which is for discerning if a resource meets the requirements another expects for an automatic edge. This is because the automatic edge system assumes a unified UID pattern to test for equality. In the future it might be helpful or sane to merge the two similar comparison functions although for now they are separate because they are actually answer different questions.

Did you know that there is a band named MGMT?

I didn't realize this when naming the project, and it is accidental. After much anguishing, I chose the name because it was short and I thought it was appropriately descriptive. If you need a less ambiguous search term or phrase, you can try using mgmtconfig or mgmt config.

You didn't answer my question, or I have a question!

It's best to ask on IRC to see if someone can help you. Once we get a big enough community going, we'll add a mailing list. If you don't get any response from the above, you can contact me through my technical blog and I'll do my best to help. If you have a good question, please add it as a patch to this documentation. I'll merge your question, and add a patch with the answer!

Reference

Please note that there are a number of undocumented options. For more information on these options, please view the source at: https://github.com/purpleidea/mgmt/. If you feel that a well used option needs documenting here, please patch it!

Overview of reference

Meta parameters

These meta parameters are special parameters (or properties) which can apply to any resource. The usefulness of doing so will depend on the particular meta parameter and resource combination.

AutoEdge

Boolean. Should we generate auto edges for this resource?

AutoGroup

Boolean. Should we attempt to automatically group this resource with others?

Noop

Boolean. Should the Apply portion of the CheckApply method of the resource make any changes? Noop is a concatenation of no-operation.

Retry

Integer. The number of times to retry running the resource on error. Use -1 for infinite. This currently applies for both the Watch operation (which can fail) and for the CheckApply operation. While they could have separate values, I've decided to use the same ones for both until there's a proper reason to want to do something differently for the Watch errors.

Delay

Integer. Number of milliseconds to wait between retries. The same value is shared between the Watch and CheckApply retries. This currently applies for both the Watch operation (which can fail) and for the CheckApply operation. While they could have separate values, I've decided to use the same ones for both until there's a proper reason to want to do something differently for the Watch errors.

Poll

Integer. Number of seconds to wait between CheckApply checks. If this is greater than zero, then the standard event based Watch mechanism for this resource is replaced with a simple polling mechanism. In general, this is not recommended, unless you have a very good reason for doing so.

Please keep in mind that if you have a resource which changes every I seconds, and you poll it every J seconds, and you've asked for a converged timeout of K seconds, and I <= J <= K, then your graph will likely never converge.

When polling, the system detects that a resource is not converged if its CheckApply method returns false. This allows a resource which changes every I seconds, and which is polled every J seconds, and with a converged timeout of K seconds to still converge when J <= K, as long as I > J || I > K, which is another way of saying that if the resource finally settles down to give the graph enough time, it can probably converge.

Limit

Float. Maximum rate of CheckApply runs started per second. Useful to limit an especially eventful process from causing excessive checks to run. This defaults to +Infinity which adds no limiting. If you change this value, you will also need to change the Burst value to a non-zero value. Please see the rate package for more information.

Burst

Integer. Burst is the maximum number of runs which can happen without invoking the rate limiter as designated by the Limit value. If the Limit is not set to +Infinity, this must be a non-zero value. Please see the rate package for more information.

Graph definition file

graph.yaml is the compiled graph definition file. The format is currently undocumented, but by looking through the examples/ you can probably figure out most of it, as it's fairly intuitive.

Command line

The main interface to the mgmt tool is the command line. For the most recent documentation, please run mgmt --help.

--yaml <graph.yaml>

Point to a graph file to run.

--converged-timeout <seconds>

Exit if the machine has converged for approximately this many seconds.

--max-runtime <seconds>

Exit when the agent has run for approximately this many seconds. This is not generally recommended, but may be useful for users who know what they're doing.

--noop

Globally force all resources into no-op mode. This also disables the export to etcd functionality, but does not disable resource collection, however all resources that are collected will have their individual noop settings set.

--remote <graph.yaml>

Point to a graph file to run on the remote host specified within. This parameter can be used multiple times if you'd like to remotely run on multiple hosts in parallel.

--allow-interactive

Allow interactive prompting for SSH passwords if there is no authentication method that works.

--ssh-priv-id-rsa

Specify the path for finding SSH keys. This defaults to ~/.ssh/id_rsa. To never use this method of authentication, set this to the empty string.

--cconns

The maximum number of concurrent remote ssh connections to run. This defaults to 0, which means unlimited.

--no-caching

Don't allow remote caching of the remote execution binary. This will require the binary to be copied over for every remote execution, but it limits the likelihood that there is leftover information from the configuration process.

--prefix <path>

Specify a path to a custom working directory prefix. This directory will get created if it does not exist. This usually defaults to /var/lib/mgmt/. This can't be combined with the --tmp-prefix option. It can be combined with the --allow-tmp-prefix option.

--tmp-prefix

If this option is specified, a temporary prefix will be used instead of the default prefix. This can't be combined with the --prefix option.

--allow-tmp-prefix

If this option is specified, we will attempt to fall back to a temporary prefix if the primary prefix couldn't be created. This is useful for avoiding failures in environments where the primary prefix may or may not be available, but you'd like to try. The canonical example is when running mgmt with --remote there might be a cached copy of the binary in the primary prefix, but in case there's no binary available continue working in a temporary directory to avoid failure.

Compilation options

You can control some compilation variables by using environment variables.

Disable livirt support

If you wish to compile mgmt without libvirt, you can use the following command:

GOTAGS=novirt make build

Examples

For example configurations, please consult the examples/ directory in the git source repository. It is available from:

https://github.com/purpleidea/mgmt/tree/master/examples

Systemd:

See misc/mgmt.service for a sample systemd unit file. This unit file is part of the RPM.

To specify your custom options for mgmt on a systemd distro:

sudo mkdir -p /etc/systemd/system/mgmt.service.d/

cat > /etc/systemd/system/mgmt.service.d/env.conf <<EOF
# Environment variables:
MGMT_SEEDS=http://127.0.0.1:2379
MGMT_CONVERGED_TIMEOUT=-1
MGMT_MAX_RUNTIME=0

# Other CLI options if necessary.
#OPTS="--max-runtime=0"
EOF

sudo systemctl daemon-reload

Development

This is a project that I started in my free time in 2013. Development is driven by all of our collective patches! Dive right in, and start hacking! Please contact me if you'd like to invite me to speak about this at your event.

You can follow along on my technical blog.

To report any bugs, please file a ticket at: https://github.com/purpleidea/mgmt/issues.

Authors

Copyright (C) 2013-2016+ James Shubin and the project contributors

Please see the AUTHORS file for more information.