Minicom to a Juniper SRX-220

Cluster computing requires a cluster of computers. For the past several years, I have been attempting to get work down without having a home cluster. This is no longer tenable, and I need to build my own.

One of the requirements for a home cluster is a progammable network device. I’ve purchased a second hand Junper SRC22.

Juniper SRX 220

Juniper SRX 220

Here are my configuration notes.
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Recursive DNS and FreeIPA

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 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 (yes I know this is not routable, just for example) my resolve.conf would look like.


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

Ansible, Azure, and Managed Disks

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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Launching Custom Image VMs on Azure With Anisble

Part of my Job is making sure our customers can run our software in Public clouds.  Recently, I was able to get CloudForms Management Engine (CFME) to deploy to Azure. Once I got it done manually, I wanted to automate the deployment, and that means Ansible.  Turns out that launching custom images from Ansible is not support int the current GA version of the Azure modules, but has been implemented upstream.

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Generating a list of URL patterns for OpenStack services.

Last year at the Boston OpenStack summit, I presented on an Idea of using URL patterns to enforce RBAC. While this idea is on hold for the time being, a related approach is moving forward building on top of application credentials. In this approach, the set of acceptable URLs is added to the role, so it is an additional check. This is a lower barrier to entry approach.
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