Category Archives: Sysadmin

Recursive DNS and FreeIPA

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DNS is essential to Kerberos. Kerberos Identity for servers is based around host names, and if you don’t have a common view between client and server, you will not be able to access your remote systems. Since DNS is an essential part of FreeIPA, BIND is one of the services integrated into the IPA server.

When a user wants to visit a public website, like this one, they click a link or type that URL into their browsers navigation bar. The browser then requests the IP address for the hostname inside the URL from the operating system via a library call. On a Linux based system, the operating system makes the DNS call to the server specified in /etc/resolv.conf. But what happens if the DNS server does not know the answer? It depends on how it is configured. In the simple case, where the server is not allowed to make additional calls, it returns a response that indicates the record is not found.

Since IPA is supposed to be the one-source-of-truth for a client system, it is common practice to register the IPA server as the sole DNS resolver. As such, it cannot just short-circuit the request. Instead, it performs a recursive search to the machines it has set up as Forwarders. For example, I often will set up a sample server that points to the google resolver at 8.8.8.8. Or, now CloudFlare has DNS privacy enabled, I might use that.

This is fine inside controlled environments, but is sub-optimal if the DNS portion of the IPA server is accessible on the public internet. It turns out that forwarding requests allows a DNS server to be used to attack these DNS servers via a distributed denial of service attack. In this attack, the attackers sends the request to all DNS servers that are acting as forwarders, and these forwarders hammer on the central DNS servers.

If you have set up a FreeIPA server on the public internet, you should plan on disabling Recursive DNS queries. You do this by editing the file /etc/named.conf and setting the values:

allow-recursion {"none";};
recursion no;

And restarting the named service.

And then everything breaks. All of your IPA clients can no longer resolve anything except the entries you have in your IPA server.

The fix for that is to add the (former) DNS forward address as a nameserver entry in /etc/resolv.conf on each machine, including your IPA server. Yes, it is a pain, but it limits the query capacity to only requests local to those machines. For example, if my IPA server is on 10.10.2.1 (yes I know this is not routable, just for example) my resolve.conf would look like.

search younglogic.com
nameserver 10.10.2.1
nameserver 1.1.1.1

If you wonder if your Nameserver has this problem, use this site to test it.

Ansible, Azure, and Managed Disks

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Many applications have a data directory, usually due to having an embedded database. For the set I work with, this includes Red Hat IdM/FreeIPA, CloudForms/ManageIQ, Ansible Tower/AWX, and OpenShift/Kubernetes. Its enough of a pattern that I have Ansible code for pairing a set of newly allocated partitions with a set of previously built virtual machines.

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Java on Port 443

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I’ve been working on setting up a Java based SAML provider. This means that the application needs to handle request and response over HTTPS. And, since often this is deployed in data centers where non-standard ports are blocked, it means that the HTTPS really needs to be supported on the proper port, which is 443. Here are the range of options.
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Java and Certmonger

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Earlier this week, I got some advice from John Dennis on how to set up the certificates for a Java based web application. The certificates were to be issued by the Dogtag instance in a Red Hat Identity Mangement (RH IdM) install. However, unlike the previous examples I’ve seen, this one did some transforms from the certificate files, into PKCS12 and then finally into the keystore. It Looks like this:

ipa-getcert request -f /etc/pki/tls/certs/rhsso-cert.pem -k /etc/pki/tls/private/rhsso-key.pem -I rhsso -K RHSSO/`hostname` -D `hostname`

openssl pkcs12 -export -name rhsso -passout pass:FreeIPA4All -in /etc/pki/tls/certs/rhsso-cert.pem -inkey /etc/pki/tls/private/rhsso-key.pem -out rhsso.p12

keytool -importkeystore -srckeystore rhsso.p12 -srcstoretype PKCS12 -srcstorepass FreeIPA4All -destkeystore keycloak.jks -deststorepass FreeIPA4All -alias rhsso

keytool -keystore keycloak.jks -import -file /etc/ipa/ca.crt -alias ipa-ca

cp keycloak.jks /etc/opt/rh/rh-sso7/keycloak/standalone/

Aside from the complications of this process, it also means that the application will not be updated when Certmonger automatically renews the certificate, leading to potential down time. I wonder if there is a better option.

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Virtualization Setup for RH CSA study

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While my company has wonderful resources to allow employees to study for our certifications, they are time limited to prevent waste. I find I’ve often kicked off the lab, only to get distracted with a reql-world-interrupt, and come back to find the lab has timed out. I like working on my own systems, and having my own servers to work on. As such, I’m setting up a complementary system to the corporate one for my own study.
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Matching Create and Teardown in an Ansible Role

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Nothing lasts forever. Except some developer setups that no-one seems to know who owns, and no one is willing to tear down. I’ve tried to build the code to clean up after myself into my provisioning systems. One pattern I’ve noticed is that the same data is required for building and for cleaning up a cluster. When I built Ossipee, each task had both a create and a teardown stage. I want the same from Ansible. Here is how I’ve made it work thus far.

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Deploying an image on OpenStack that is bigger than the available flavors.

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Today I tried to use our local OpenStack instance to deploy CloudForms Management Engine (CFME). Our OpenStack deployment has a set of flavors that all are defined with 20 GB Disks. The CFME image is larger than this, and will not deploy on the set of flavors. Here is how I worked around it.
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Freeing up a Volume from a Nova server that errored

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Trial and error. Its a key part of getting work done in my field, and I make my share of errors. Today, I tried to create a virtual machine in Nova using a bad glance image that I had converted to a bootable volume:

The error message was:

 {u'message': u'Build of instance d64fdd07-748c-4e27-b212-59e8cef9d6bf aborted: Block Device Mapping is Invalid.', u'code': 500, u'created': u'2018-01-31T03:10:56Z'}

The VM could not release the volume.

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Creating an Ansible Inventory file using Jinja templating

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While there are lots of tools in Ansible for generating an inventory file dynamically, in a system like this, you might want to be able to perform additional operations against the same cluster. For example, once the cluster has been running for a few months, you might want to do a Yum update. Eventually, you want to de-provision. Thus, having a remote record of what machines make up a particular cluster can be very useful. Dynamic inventories can be OK, but often it takes time to regenerate the inventory, and that may slow down an already long process, especially during iterated development.

So, I like to generate inventory files. These are fairly simple files, but they are not one of the supported file types in Ansible. Ansible does support ini files, but the inventory files have maybe lines that are not in key=value format.

Instead, I use Jinja formatting to generate inventory files, and they are pretty simple to work with.

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