Cfg

The Cfg plugin provides a repository to describe configuration file contents for clients. In its simplest form, the Cfg repository is just a directory tree modeled off of the directory tree on your client machines.

The Cfg Repository

The Cfg plugin is enabled by including Cfg on the plugins line of the [server] section of your Bcfg2 server config file. The repository itself lives in /var/lib/bcfg2/Cfg, assuming you are using the default repository location of /var/lib/bcfg2. The contents of this directory are a series of directories corresponding to the real-life locations of the files on your clients, starting at the root level. For example:

% ls Cfg
bin/  boot/  etc/  opt/  root/  usr/  var/

Specific config files go in like-named directories in this heirarchy. For example the password file, /etc/passwd, goes in Cfg/etc/passwd/passwd, while the ssh pam module config file, /etc/pam.d/sshd, goes in Cfg/etc/pam.d/sshd/sshd. The reason for the like-name directory is to allow multiple versions of each file to exist, as described below. Note that these files are exact copies of what will appear on the client machine (except when using templates – see below).

Group-Specific Files

It is often the case that you want one version of a config file for all of your machines except those in a particular group. For example, /etc/fstab should look alike on all of your desktop machines, but should be different on your file servers. Bcfg2 can handle this case through use of group-specific files.

As mentioned above, all Cfg entries live in like-named directories at the end of their directory tree. In the case of fstab, the file at Cfg/etc/fstab/fstab will be handed out by default to any client that asks for a copy of /etc/fstab. Group-specific files are located in the same directory and are named with the following syntax:

/path/to/filename/filename.GNN_groupname

NN is a priority number where 00 is lowest and 99 is highest, and groupname is the name of a group defined in Metadata/groups.xml. Back to our fstab example, we might have a Cfg/etc/fstab/ directory that looks like this:

fstab
fstab.G50_server
fstab.G99_fileserver

By default, clients will receive the plain fstab file when they request /etc/fstab. Any machine that is in the server group, however, will instead receive the fstab.G50_server file. Finally, any machine that is in the fileserver group will receive the fstab.G99_fileserver file, even if they are also in the server group.

Host-Specific Files

Similar to the case with group-specific files, there are cases where a specific machine should have a different version of a file than all others. This can be accomplished with host-specific files. The format of a host-specific file name is:

/path/to/filename/filename.H_host.example.com

Host-specific files have a higher priority than group specific files. Again, the fstab example:

fstab
fstab.G50_server
fstab.G99_fileserver
fstab.H_host.example.com

In this case, host.example.com will always get the host-specific version, even if it is part of the server or fileserver (or both) classes.

Note

If you have the ability to choose between using a group-specific and a host-specific file, it is almost always best to use a group-specific one. That way if a hostname changes or an extra copy of a particular client is built, it will get the same changes as the original.

Templates

Genshi Templates

Genshi templates allow you to use the Genshi templating system. Genshi templates should be named with a .genshi extension, e.g.:

% ls Cfg/etc/motd
info.xml  motd.genshi

See the genshi documentation for examples of Genshi syntax.

Troubleshooting

When developing a template, you can see what the template would generate on a client with bcfg2-info:

bcfg2-info buildfile <path> <hostname>

E.g.:

bcfg2-info buildfile /etc/foo.conf foo.example.com

To generate a file with an altsrc attribute, you can run:

bcfg2-info buildfile /etc/foo/foo.conf --altsrc=/etc/foo.conf \
    foo.example.com

Sometimes, it’s useful to be able to do more in-depth troubleshooting by running the template manually. To do this, run bcfg2-info debug, and, once in the Python interpreter, run:

metadata = self.build_metadata("<hostname>")
source_path = "<full path to template>"
name = source_path[len(self.setup['repo']):]

Then, run:

import os
from genshi.template import TemplateLoader, NewTextTemplate
template = TemplateLoader().load(source_path, cls=NewTextTemplate)
data = dict(metadata=metadata,
            source_path=source_path,
            path=source_path,
            name=name,
            repo=self.setup['repo'])
print(template.generate(**data).render())

This gives you more fine-grained control over how your template is rendered. E.g., you can tweak the values of the variables passed to the template, or evaluate the template manually, line-by-line, and so on.

You can also use this approach to render templates that depend on altsrc tags by setting source_path to the path to the template, and setting name to the path to the file to be generated, e.g.:

metadata = self.build_metadata("foo.example.com")
source_path = "/Cfg/etc/sysconfig/network-scripts/ifcfg-template/ifcfg-template.genshi"
name = "/etc/sysconfig/network-scripts/ifcfg-bond0"

Error handling

Situations may arise where a templated file cannot be generated due to missing or incomplete information. A TemplateError can be raised to force a bind failure and prevent sending an incomplete file to the client. For example, this template:

{% python
    from genshi.template import TemplateError
    grp = None
    for g in metadata.groups:
        if g.startswith('ganglia-gmond-'):
            grp = g
            break
    else:
        raise TemplateError, "Missing group"
%}\

will fail to bind if the client is not a member of a group starting with “ganglia-gmond-“. The syslogs on the server will contain this message:

bcfg2-server[5957]: Genshi template error: Missing group
bcfg2-server[5957]: Failed to bind entry: Path /etc/ganglia/gmond.conf

…indicating the bind failure and message raised with the TemplateError.

Handling Dollar Signs

In a Genshi template, $ is a special character and must be escaped by doubling, i.e., $$. For instance, to embed the Subversion $Id$ keyword in a Genshi template, you would have to do $$Id$$.

Examples

• bcfg2-cron
• clients.xml
• ganglia
• grub.conf
• hosts
• iptables
• motd
• my.cnf
• test

Cheetah Templates

Cheetah templates allow you to use the cheetah templating system. Cheetah templates should be named with a .cheetah extension, e.g.:

% ls Cfg/etc/motd
info.xml  motd.cheetah

Examples

• Writing crontab with Cheetah
• Basic Cheetah Templates

Comments and Cheetah

As Cheetah processes your templates it will consider hash “#” style comments to be actual comments in the template and will strip them from the final config file. If you would like to preserve the comment in the final config file you need to escape the hash character ‘#’ which will tell Cheetah (and Python) that you do in fact want the comment to appear in the final config file.:

# This is a comment in my template which will be stripped when it's processed through Cheetah
\# This comment will appear in the generated config file.

Jinja2 Templates

Jinja2 templates allow you to use the jinja2 templating system. Jinja2 templates should be named with a .jinja2 extension, e.g.:

% ls Cfg/etc/motd
info.xml  motd.jinja2

Examples

• Extending Jinja2 Templates
• Including Jinja2 Templates
• Basic Jinja2 Templates

Inside Templates

Several variables are pre-defined inside templates:

Name	Description
metadata	Client metadata
name	The value of the name attribute as specified in the Path entry in Bcfg2.
source_path	The path to the template file on the filesystem
repo	The path to the Bcfg2 repository on the filesystem
path	In Genshi templates, path is a synonym for source_path. In Cheetah templates and Jinja2 templates, it’s a synonym for name. For this reason, use of path is discouraged, and it may be deprecated in a future release.

To access these variables in a Genshi template, you can simply use the name, e.g.:

Path to this file: ${name}

Similarly, in a Jinja2 template:

Path to this file: {{ name }}

In a Cheetah template, the variables are properties of self, e.g.:

Path to this file: $self.name

Notes on Using Templates

Templates can be host and group specific as well. Deltas will not be processed for any Genshi, Cheetah, or Jinja2 base file.

Note

If you are using templating in combination with host-specific or group-specific files, you will need to ensure that the .genshi .cheetah or .jinja2 extension is at the end of the filename. Using the examples from above for host.example.com and group server you would have the following:

Cfg/etc/fstab/fstab.H_host.example.com.genshi
Cfg/etc/fstab/fstab.G50_server.cheetah

You can mix Genshi and Cheetah when using different host-specific or group-specific files. For example:

Cfg/etc/fstab/fstab.H_host.example.com.genshi
Cfg/etc/fstab/fstab.G50_server.cheetah

Encrypted Files

New in version 1.3.0.

Bcfg2 allows you to encrypt files stored in Cfg/ to protect the data in them from other people who need access to the repository. See also Encrypted Properties data for information on encrypting elements in Properties files, which is often more friendly for tracking changes in a VCS.

Note

This feature is not intended to secure the files against a malicious attacker who has gained access to your Bcfg2 server, as the encryption passphrases are held in plaintext in bcfg2.conf. This is only intended to make it easier to use a single Bcfg2 repository with multiple admins who should not necessarily have access to each other’s sensitive data.

See Bcfg2 Data Encryption for more details on encryption in Bcfg2 in general.

Encrypting Files

An encrypted file should end with .crypt, e.g.:

Cfg/etc/foo.conf
Cfg/etc/foo.conf/foo.conf.crypt
Cfg/etc/foo.conf/foo.conf.G10_foo.crypt

Encrypted Genshi, Cheetah, and Jinja2 templates can have the extensions in either order, e.g.:

Cfg/etc/foo.conf/foo.conf.crypt.genshi
Cfg/etc/foo.conf/foo.conf.G10_foo.genshi.crypt
Cfg/etc/foo.conf/foo.conf.H_bar.example.com.crypt.cheetah

To encrypt or decrypt a file, use bcfg2-crypt.

SSH Keys

New in version 1.3.0.

Cfg can also be used to automatically create and distribute SSH key pairs and the authorized_keys file.

Keys can be created one of two ways:

• Host-specific keys, where each client has its own key pair. This is the default.
• Group-specific keys. To do this, you must set category in either bcfg2.conf (see “Configuration” below) or in privkey.xml. Keys created for a given client will be specific to that client’s group in the specified category.

Group-specific keys are useful if, for instance, you have multiple distinct environments (development, testing, production, for example) and want to maintain separate keys for each environment.

This feature actually creates static keys, much like the SSHbase plugin creates SSH certificates. It doesn’t generate them on the fly for each request; it generates the key once, then saves it to the filesystem.

Creating key pairs

To create an SSH key pair, you need to define how the private key will be created in privkey.xml. For instance, to create /home/foo/.ssh/id_rsa, you would create /var/lib/bcfg2/Cfg/home/foo/.ssh/id_rsa/privkey.xml.

This will create both the private key and the public key; the latter is created by appending .pub to the private key filename. It is not possible to change the public key filename.

You may optionally also create a corresponding pubkey.xml, which will allow the key pair to be created when the public key is requested. (For the example above, you’d create /var/lib/bcfg2/Cfg/home/foo/.ssh/id_rsa.pub/pubkey.xml. This can speed up the propagation of SSH keys throughout your managed systems, particularly if you use the authorized_keys generation feature.

privkey.xml

privkey.xml contains a top-level PrivateKey element, and is structured as follows:

See Bcfg2 Data Encryption for more details on encryption in Bcfg2 in general.

pubkey.xml

pubkey.xml only ever contains a single line:

<PublicKey/>

It acts only as a flag to Bcfg2 that a key pair should be generated, if none exists, using the associated privkey.xml file. The path to privkey.xml is determined by removing .pub from the directory containing pubkey.xml. I.e., if you create /var/lib/bcfg2/Cfg/home/foo/.ssh/id_rsa.pub/pubkey.xml, then Bcfg2 will use /var/lib/bcfg2/Cfg/home/foo/.ssh/id_rsa/privkey.xml to create the key pair.

Use of pubkey.xml is optional, but is recommended. If you do not use pubkey.xml files, you may encounter two problems:

• On the first Bcfg2 client run on a given client, the private keys may be present but the public keys may not be. This will be fixed by running bcfg2 again.
• If you are including an automatically created public key in authorized_keys, it will not be created until the client the key is for requests the key pair.

As an example of this latter scenario, suppose that your authorized_keys.xml allows access to foo.example.com from /root/.ssh/id_rsa.pub for bar.example.com. If bar.example.com has not run the Bcfg2 client, then no key pair will have been generated, and generating the foo.example.com authorized_keys file will create a warning. But if you create Cfg/root/.ssh/id_rsa.pub/pubkey.xml, then building authorized_keys for foo.example.com will create root’s keypair for bar.example.com.

Note

In order to use pubkey.xml, there must be a corresponding privkey.xml. You cannot, for instance, populate a directory with manually-generated private SSH keys, drop pubkey.xml in the related public key directory, and expect Bcfg2 to generate the public keys. It will not.

Examples

privkey.xml can, at its simplest, be very simple indeed:

<PrivateKey/>

This will create a private key with all defaults. Or it can be more complex:

<PrivateKey category="environment">
  <Params bits="1024" type="dsa"/>
  <Group name="secure">
    <Passphrase encrypted="secure">U2FsdGVkX19xACol83uyPELP94s4CmngD12oU6PLLuE=</Passphrase>
  </Group>
</PrivateKey>

This creates a 1024-bit DSA key for each group in the environment category, and keys for clients in the secure group will be protected with the given (encrypted) passphrase.

To complete the example, assume that this file was saved at /var/lib/bcfg2/Cfg/home/foo/.ssh/id_rsa/privkey.xml. If a client in the development group, which is a group in the environment category, requests the private key, then the following files would be created:

/var/lib/bcfg2/Cfg/home/foo/.ssh/id_rsa/id_rsa.G50_development
/var/lib/bcfg2/Cfg/home/foo/.ssh/id_rsa.pub/id_rsa.pub.G50_development

/var/lib/bcfg2/Cfg/home/foo/.ssh/id_rsa.pub would be created if it did not exist.

Subsequent clients that were also members of the development environment would get the keys that have already been generated.

pubkey.xml always contains a single empty tag:

<PublicKey/>

Generating authorized_keys

authorized_keys can be automatically generated from public SSH keys that exist in the Cfg tree. The keys in question can be generated from privkey.xml, or they can be manually created.

If a key doesn’t exist when authorized_keys is generated, the key will only be created if pubkey.xml exists. If that is not the case, a warning will be produced.

To generate authorized_keys, create authorized_keys.xml, e.g.: /var/lib/bcfg2/Cfg/root/.ssh/authorized_keys/authorized_keys.xml.

authorized_keys.xml

authorized_keys.xml is structured as follows:

Example

<AuthorizedKeys>
  <Group name="some_group">
    <Allow from="/root/.ssh/id_rsa.pub"/>
    <Allow from="/root/.ssh/id_rsa.pub" group="test"/>
  </Group>
  <Allow from="/root/.ssh/id_rsa.pub" host="foo.example.com"/>
  <Allow from="/home/foo_user/.ssh/id_rsa.pub">
    <Option name="command" value="/home/foo_user/.ssh/ssh_command_filter"/>
    <Option name="no-X11-forwarding"/>
  </Allow>
  <Allow>
    ssh-rsa AAAAB3NzaC1yc2EAAAADAQABAAABAQDw/rgKQeARRAHK5bQQhAAe1b+gzdtqBXWrZIQ6cIaLgxqj76TwZ3DY4A6aW9RgC4zzd0p4a9MfsScUIB4+UeZsx9GopUj4U6H8Vz7S3pXxrr4E9logVLuSfOLFbI/wMWNRuOANqquLYQ+JYWKeP4kagkVp0aAWp7mH5IOI0rp0A6qE2you4ep9N/nKvHDrtypwhYBWprsgTUXXMHnAWGmyuHGYWxNYBV9AARPdAvZfb8ggtuwibcOULlyK4DdVNbDTAN1/BDBE1ve6WZDcrc386KhqUGj/yoRyPjNZ46uZiOjRr3cdY6yUZoCwzzxvm5vle6mEbLjHgjGEMQMArzM9 vendor@example.com
  </Allow>
</AuthorizedKeys>

Note

authorized_keys.xml allows you to specify the group whose public key should be allowed. This retrieves the public key specific to that group (if it exists), not the public key for all hosts in that group. This is due to the performance penalties that would be imposed by that approach.

Similarly, it is not possible to allow access from all keys for a given user (i.e., at a given path).

Hopefully, the performance concerns can be resolved in a future release and these features can be added.

SSL Keys and Certificates

Cfg can also create SSL keys and certs on the fly, and store the generated data in the repo so that subsequent requests do not result in repeated key/cert recreation. In the event that a new key or cert is needed, the old file can simply be removed from the repository, and the next time that host checks in, a new file will be created. If that file happens to be the key, any dependent certificates will also be regenerated.

See also Automated Bcfg2 SSL Authentication for a detailed example that uses the SSL key management feature to automate Bcfg2 certificate authentication.

Getting started

In order to use the SSL certificate generation feature, you must first have at least one CA configured on your system. For details on setting up your own OpenSSL based CA, please see http://www.openssl.org/docs/apps/ca.html for details of the suggested directory layout and configuration directives.

For SSL cert generation to work, the openssl.cnf (or other configuration file) for that CA must contain full (not relative) paths.

1. Add a section to your /etc/bcfg2.conf called sslca_foo, replacing foo with the name you wish to give your CA so you can reference it in certificate definitions. (If you only have one CA, you can name it sslca_default, and it will be the default CA for all other operations.)

2. Under that section, add a config option that gives the location of the openssl.cnf file for your CA.

3. If necessary, add a passphrase option containing the passphrase for the CA’s private key. If no passphrase is entry exists, it is assumed that the private key is stored unencrypted.

4. Optionally, add a chaincert option that points to the location of your ssl chaining certificate. This is used when preexisting certificate hostfiles are found, so that they can be validated and only regenerated if they no longer meet the specification. If you’re using a self signing CA this would be the CA cert that you generated. If the chain cert is a root CA cert (e.g., if it is a self-signing CA), also add an entry root_ca = true. If chaincert is omitted, certificate verification will not be performed.

5. Once all this is done, you should have a section in your /etc/bcfg2.conf that looks similar to the following:

   [sslca_default]
   config = /etc/pki/CA/openssl.cnf
   passphrase = youReallyThinkIdShareThis?
   chaincert = /etc/pki/CA/chaincert.crt
   root_ca = true
   

6. You are now ready to create key and certificate definitions. For this example we’ll assume you’ve added Path entries for the key, /etc/pki/tls/private/localhost.key, and the certificate, /etc/pki/tls/certs/localhost.crt to a bundle.

7. Within the Cfg/etc/pki/tls/private/localhost.key directory, create a sslkey.xml file containing the following:

   <KeyInfo/>
   

8. This will cause the generation of an SSL key when a client requests that Path. (By default, it will be a 2048-bit RSA key; see sslkey.xml for details on how to change the key type and size.)

9. Similarly, create sslcert.xml in Cfg/etc/pki/tls/certs/localhost.crt/, containing the following:

   <CertInfo>
     <Cert key="/etc/pki/tls/private/localhost.key" ca="foo"/>
   </CertInfo>
   

10. When a client requests the cert path, a certificate will be generated using the key hostfile at the specified key location, using the CA matching the ca attribute. ie. ca="foo" will match [sslca_default] in your /etc/bcfg2.conf

The Bcfg2 bundle example contains entries to automate the process of setting up a CA.

Configuration

bcfg2.conf

In bcfg2.conf, you must declare your CA(s) in [sslca_<name>] sections. At least one is required. Valid options are detailed below, in Cfg Configuration.

Only the config option is required; i.e., the simplest possible CA section is:

[sslca_default]
config = /etc/pki/CA/openssl.cnf

sslcert.xml

Example

<CertInfo>
  <subjectAltName>test.example.com</subjectAltName>
  <Group name="apache">
    <Cert key="/etc/pki/tls/private/foo.key" days="730"/>
  </Group>
  <Group name="nginx">
    <Cert key="/etc/pki/tls/private/foo.key" days="730"
          append_chain="true"/>
  </Group>
</CertInfo>

sslkey.xml

Example

<KeyInfo>
  <Group name="fast">
    <Key type="rsa" bits="1024"/>
  </Group>
  <Group name="secure">
    <Key type="rsa" bits="4096"/>
  </Group>
</KeyInfo>

Content Validation

To ensure that files with invalid content are not pushed out, you can provide a content validation script that will be run against each file. Create a file called :test inside the directory for the file you want to test. For example:

Cfg/etc/sudoers/:test

You can also create host- and group-specific validators:

Cfg/etc/sudoers/:test.G80_foogroup
Cfg/etc/sudoers/:test.H_bar.example.com

A validator script has the following attributes:

• It must be executable, or specify a valid bangpath;
• The entire content of the file is passed to the validator on stdin;
• The validator is not called with any flags or arguments;
• The validator must return 0 on success and non-zero on failure; and
• The validator must output a sensible error message on failure.

For sudoers, a very simple validator is:

#!/bin/sh
visudo -cf -

This uses the visudo command’s built-in validation.

If you wish to disable validation, this can be done with the following setting in bcfg2.conf:

[cfg]
validation=no

If you have a very large number of validators, you may wish to disable validation by default to avoid slowing down the generation of configurations on the server, and use bcfg2-test (for instance, as a post-commit hook or as part of a code review process) to run validation. You can do this by setting validation=no in bcfg2.conf as described above, and then calling bcfg2-test with the --cfg-validation flag.

File permissions

File permissions for entries handled by Cfg are controlled via the use of info.xml files. Note that you cannot use both a Permissions entry and a Path entry to handle the same file.

Cfg Configuration

The behavior of many bits of the Cfg plugin can be configured in bcfg2.conf with the following options.

In addition to privkey.xml and authorized_keys.xml, described above, the behavior of the SSH key generation feature can be influenced by several options in the [sshkeys] section of bcfg2.conf:

Section	Option	Description	Values	Default
cfg	passphrase	Use the named passphrase to encrypt created data on the filesystem. (E.g., SSH and SSL keys.) The passphrase must be defined in the [encryption] section.	String	None
cfg	category	Generate data (e.g., SSH keys, SSL keys and certs) specific to groups in the given category. It is best to pick a category that all clients have a group from.	String	None
cfg	validation	Whether or not to perform Content Validation specific to groups in the given category. It is best to pick a category that all clients have a group from.	Boolean	True
sshkeys	passphrase	Override the global Cfg passphrase with a specific passphrase for encrypting created SSH private keys.	String	None
sshkeys	category	Override the global Cfg category with a specific category for created SSH keys.	String	None
sslca	passphrase	Override the global Cfg passphrase with a specific passphrase for encrypting created SSL keys.	String	None
sslca	category	Override the global Cfg category with a specific category for created SSL keys and certs.	String	None
sslca_*	config	Path to the openssl config for the CA	String	None
sslca_*	passphrase	Passphrase for the CA private key	String	None
sslca_*	chaincert	Path to the SSL chaining certificate for verification	String	None
sslca_*	root_ca	Whether or not <chaincert> is a root CA (as opposed to an intermediate cert)	Boolean	False

See Bcfg2 Data Encryption for more details on encryption in Bcfg2 in general.