Clustering on Luther Monson

A Lock Is Only as Good as Its Release

Tue, 13 Oct 2026 20:40:00 -0700

Every “build a lock on Redis” tutorial spends its time on acquisition: SET key value NX PX 30000, one winner, done. The release gets one line, DEL key. That line is where most of the lock bugs I’ve had in ePHPm lived. Over about three months the same mistake showed up in three places. First the native session handler, then two of the Composer wrapper packages, and finally the cluster. Each time it wore a slightly different costume.

Clustered SQLite in ePHPm, Part 3: CDC Over the Cluster Channel

Tue, 15 Sep 2026 21:08:00 -0700

By the end of Part 2 ePHPm v0.7.0 ran exactly one SQLite engine in process. That was Turso, for single-node and clustered mode alike. The sidecar was gone. What I skipped over is how a replica actually gets the primary’s writes, and what happens when the primary dies with data on it. That’s this post.

Part 1: Replication by sidecar with sqld
Part 2: Adding Turso
Part 3: CDC over the cluster channel (this post)

CDC from the engine itself

Turso has change data capture built in. Turn it on for a connection and every committed change lands in a turso_cdc table. Each row has a monotonically increasing change_id, the table, the rowid, and before/after images of the record. The primary tails that table and ships transaction batches. Replicas apply them. That’s the whole design. It landed as an experimental path in #186 at the end of July. The tailer and applier live in litewire (litewire#10).

Clustered ACME in Production: Three Bugs That Took TLS Down

Wed, 02 Sep 2026 19:30:00 -0700

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 TLS down. None of them showed up in a unit test. All of them are the kind of thing you only learn by putting the feature on real machines.

Clustered SQLite in ePHPm, Part 1: Replication by Sidecar

Sat, 08 Aug 2026 20:14:00 -0700

Most PHP sites I have run in the last twenty years did not need a MySQL server. They needed a database, and MySQL was the one every framework spoke. With ePHPm I have been trying to get rid of that server for the common case. The piece that makes it possible is litewire. PHP connects with plain pdo_mysql. litewire speaks the MySQL wire protocol, and the queries land in a SQLite file. WordPress and Laravel don’t know the difference. No mysqld, no child processes, just ephpm and a .db file.

Gossip-Based Clustering for PHP Apps

Tue, 04 Aug 2026 20:52:00 -0700

Most PHP developers never touch clustering primitives. That’s by design. PHP is share-nothing. Each request starts from zero, and anything shared lives somewhere else. Sessions go in Redis. Cache goes in Redis or Memcached. Locks go in Redis. When you run two app servers, the “cluster” is really two stateless boxes pointed at the same Redis. That works until Redis is the thing you’re trying not to run.

ePHPm has its own KV store in the same process as PHP. On one node that’s straightforward. On three nodes behind a load balancer, a session written on node 1 has to be readable on node 3. That means the nodes have to know about each other and agree on where data lives. This post is how that works as of v0.5.2, including the parts I’m not happy with yet.