jschoubben
e89379fef8
The mesh generates a password, seals it to the machine that must accept it, and discards the plaintext — so it cannot tell PostgreSQL to start accepting it. Something on that machine reads what the host wrote and makes it true. Everything up to that step is proven elsewhere; this is where a password either becomes a login or does not. A scenario with one machine and a database, and six assertions: the password works, running again reaches the same state and says nothing, rotation makes the new one work and the old one stop, a departed consumer loses its login, a role nobody here made is left alone, and a manifest naming a credential that was never written is refused rather than creating a login with no password. Each was confirmed to fail — and only it to fail — with the behaviour removed from the provisioner: only-creates breaks rotation, no-revoke breaks revocation, revoking everything breaks the bystander role, and ignoring a missing credential breaks the refusal. Two faults in the test itself, both worth recording: - it checked logins from inside the database's own container over 127.0.0.1, which PostgreSQL's default pg_hba trusts. No password was ever verified. Demonstrated directly: over loopback a deliberately wrong password still returns a row. Only the rotation assertion noticed, because it is the one that requires a password to STOP working — which is an argument for writing that assertion every time. - the fix then read .NetworkSettings.IPAddress, which docker 29 no longer populates. It templates to empty, psql falls back to a unix socket that is not there, and every login looks impossible rather than misconfigured.
Provisioners
The half that makes a credential real.
The mesh generates a password, seals it to the machine that must accept it, and never holds the value — so it cannot tell PostgreSQL, or MinIO, or a broker, to start accepting it. Something on that machine reads what arrived and makes it true. That something is a provisioner, and it belongs to the module that ships the software, not to the mesh.
What the mesh owns is the contract. A provider module declares:
{
"provides": [{"name": "database", "scope": "mesh"}],
"receives": {"database": "/var/lib/postgres/grants/mesh.json"},
"grants": {"database": "/var/lib/postgres/grants"}
}
and is then given, by the host, from an ordinary declaration:
mesh.json |
every consumer, what it asked for, and where its credential is |
<node>.secret |
one consumer's password, alone in the file, sealed in transit and written in plain by the host |
Two files rather than one because the mesh discarded the plaintext and cannot compose a document containing it. The consequence is a good one: the readable half stays readable, and the secret half changes only when the secret does.
A provisioner reconciles; it is not told what changed. It runs after every declaration and must reach the same state from wherever it starts. That means, in order:
- every consumer in the manifest has what it asked for, with the password it was given — set every time, not only on creation, or a rotation reports success and changes nothing
- everything this provisioner made that is no longer asked for is removed. A consumer that goes away otherwise leaves a working login behind for ever, and nothing says so
Step 2 is the half usually missing, and it is the same rule the host follows about removing what it declared and no longer declares.
The reference implementation lives in mesh-control/examples/postgres-provisioner, because that
is where the contract is defined and where the language is already set up to read it. The lab's
job is the other half: raising a real PostgreSQL and proving that what the mesh delivered becomes
a login that works, a rotation that takes effect, and a revocation that bites.
Set MESH_LAB_PROVISIONER to a built one to run those.