Category Archives: Sysadmin

DHCP Lease Design

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The key piece of persisted data in an DHCP server is the lease. A lease is a the mapping between a MAC address and an IP address, limited in time. A Lease typically has a start time and an end time, but can be renewed. Because I am still living in an IPV4 world, I have to deal with arbitrarily small pools of IP addresses. Thus, the design needs to strike the balance between static and dynamic: a machine should generally get back the same IP address each time. However, if addresses get tight, address reuse should be aggressive.

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Extract Function Refactoring using inline functions.

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The Extract Function refactoring is the starting point for much of my code clean up. Once a “Main” function gets sufficiently complicated, I pull pieces of it out into their own functions, often with an eye to making them methods of the involved classes.

While working with some rust code, I encountered an opportunity to execute this refactoring on some logging code. Here’s how I executed it.

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Podman login to a secured registry

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I took the container registry I ran via podman and put it behind an Apache HTTPD instance secured with mod_ssl. Now when I try to log in to it, I get:

error authenticating creds for “nuzleaf.home.younglogic.net”: error pinging docker registry nuzleaf.home.younglogic.net: invalid status code from registry 403 (Forbidden)

Here’s my debugging notes.

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Running git and gitweb in a container with Fedora

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There are many reasons to run a web service in a container. One of the remote services I rely on most heavily is git. While git local operations are fine in a global namespace, running a shared git repository on a remote server is a web-service based use case. There are three protocols used most commonly to remotely access git: git, ssh, and https. I am going to focus on the last one here.

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Running a Container Registry Behind Apache HTTPD

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I had originally run my container registry using a self signed certificate like this:

podman run --name mirror-registry -p 4000:5000     -v /opt/registry/data:/var/lib/registry:z      -v /opt/registry/auth:/auth:z      -e "REGISTRY_AUTH=htpasswd"      -e "REGISTRY_AUTH_HTPASSWD_REALM=Registry Realm"      -e REGISTRY_AUTH_HTPASSWD_PATH=/auth/htpasswd      -v /opt/registry/certs:/certs:z      -e REGISTRY_HTTP_TLS_CERTIFICATE=/certs/domain.crt      -e REGISTRY_HTTP_TLS_KEY=/certs/domain.key      -e REGISTRY_COMPATIBILITY_SCHEMA1_ENABLED=true -d docker.io/library/registry:2

But now that I am using FreeIPA for my Bastion host, I want to use the IPA CA cert for signing the HTTPS request. The easiest thing to do is to run the registry in the container still, but then to front it with mod_proxy.

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Syncing and Serving Yum Repos on RHEL 8

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My Lab machines do not have direct access to the internet. This mirrors how my customers tend to run their environments. Instead, I run a single bastion host that can connect to the internet, and use that to perform all operations on my lab machines.

While it is great to be able to use the Install media to add packlages to PXE booted systems, after some time, the set of packages available is older than you want. For example, I hit a bug that required an update of Network Manager. So, I want to make a local yum repo from my RHEL 8 subscription. RHEL 8 makes this fairly easy.

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Network Policy to Explicitly Allow access from all Namespaces

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The Default network policy in OpenShift allows all access from all pods in all namespaces via the cluster IP. However, once you start enforcing policy on a project, all policy decision need to be made explicit. If you want to still allow access from all projects, you can use the following policy file.

kind: NetworkPolicy
apiVersion: networking.k8s.io/v1
metadata:
  name: allow-all-namespaces
spec:
  ingress:
  - from:
    - namespaceSelector: {}