Every shipmates crew member runs shell commands. Before any of them runs, it goes through a permission gate. The gate uses the same rule syntax as Claude Code settings: Bash(git status), Bash(rm *), Write(**/.claude/settings.json). The rules are merged from several layers:

GitHub Actions has a container: key that runs a job’s steps inside an image of your choosing. It’s popular because it gives you a reproducible toolchain without building a custom runner image. On a self-hosted runner it works by having the runner drive Docker. On ephemerd, “Docker” is a shim that speaks the Docker API and creates containers in containerd. Getting bind mounts right through that shim took four PRs in a week. A couple of months later the version that worked…

ePHPm can serve a directory full of sites out of one process. Point sites_dir at a folder and every subdirectory is a virtual host. The Host header decides which one you get. That’s how the PR preview environment runs. Every pull request gets a subdomain, and the code behind it is whatever somebody pushed. One process holding many tenants means ePHPm enforces every per-tenant boundary itself, in-process. There’s no container wall between site A and site B unless you add one.

php-fpm has a property nobody thinks about until they leave it. When a worker segfaults, you lose one request. The master forks a new child and life goes on. ePHPm runs every tenant’s PHP as threads inside one process. That’s where the memory and latency wins come from. It also means one tenant’s segfault takes down every other tenant on the box.

ePHPm gets its own certificates from Let’s Encrypt. In a cluster only one node should be talking to the CA. The nodes elect an ACME leader over the shared KV store. The leader orders the cert, and everybody else installs it from KV. That all had unit tests and had worked on single nodes for months. Then I tried to move wildcard TLS termination for our preview environment off a separate proxy and onto the 3-node cluster itself. In about two days it found three separate bugs that each took…

In multi-tenant mode ePHPm serves every site in sites_dir from one process. Every tenant’s PHP runs as the same OS user on the same pool of ZTS threads. A thread that just served blog.example will serve shop.example a few milliseconds later. That’s the density win. It also means the kernel has no idea which tenant is behind a given connect(). As far as Linux is concerned it’s all ephpm-web.

litewire is the piece of ePHPm that lets PHP apps talk MySQL to a SQLite file. I wrote about how it works and about the MySQL quirks WordPress depends on. This one is the less visible half of August:

After a week of Windows firewall rules that listed fine and enforced nothing, I went back to the Linux side of ephemerd feeling pretty good about it. iptables is the boring, well-understood one. Then I looked at the packet counters on a live node. I found a rule that had never matched a packet in its life. That node had pushed 9.8 GB through the same chain.

ephemerd runs CI jobs from pull requests. One of the rules is that a job can reach the internet but not my LAN. On Linux that’s a few iptables rules in the FORWARD path, and I didn’t think about it much. On Windows I spent about a week finding out how many ways there are to write a firewall rule that Windows accepts, lists and never applies.