shep-deploy-0.2.0 is not a library.

shep-deploy

A deploy dog for shep.

Watches a git branch, builds a release in an isolated directory, swaps to it, reloads the sheep, and rolls back on its own if the new release does not come up.

It is an external dog, the same shape as shep-log-rotate: an ordinary binary you adopt, talking to the daemon over the socket the CLI already uses.

Install

cargo install shep-deploy
shep adopt shep-deploy

shep adopt registers it with the shepherd, which supervises it from then on. shep dogs lists what you have adopted.

Telling it how to build

The build command lives in the deployed repository's own Flockfile, under the table shep keeps for a dog's config:

[[app]]
name = "web"
script = "server.js"

[dog.deploy.build]
command = "npm ci && npm run build"
artifacts = ["dist/bundle.js"]

shep reads nothing under dog and validates none of it. It only had to stop refusing the document for carrying it, which it does as of 0.1.10, so the same Flockfile now registers with shep start and tells this dog how to build.

That is a change from earlier versions, which put the block at the top level as [build]. shep refused a Flockfile with an unknown top-level key, so an operator following these instructions could not register their app at all. A top-level [build] is now refused here by name, pointing at the new spelling, rather than ignored and silently building nothing.

What one deploy does

Fetch into a bare clone, and compare the branch head to the last deployed sha.
git worktree add the new sha, sharing the object store.
Symlink the shared files in: whatever git ignores and .shepignore does not.
Run the build, as the app's user if it sets one.
rename(2) current onto the new release.
Reload the sheep.
Verify. On failure, put current back and reload again.

Steps 1 to 4 never touch the running app. A build that fails costs a directory, not an outage.

Verification waits for a new process to reach Online, not for any process to be Online. shep answers a reload before it has finished one, and keeps the old instance when the replacement never becomes ready, so "something is online" is true throughout a deploy that failed.

Layout

Everything lives under $SHEP_HOME/deploy/<sheep>/:

git/                 one bare clone, shared by every release
releases/<sha>/      a worktree per release
current -> releases/<sha>
deploy.toml          remote, branch, deployed sha, held sha, verify mode, watch mode

The sheep's cwd is current, permanently. Set it explicitly when you register the app: a Flockfile cwd left to default is resolved at registration, which pins the sheep to one release and makes every later swap invisible to it.

Commands

shep-deploy deploy <sheep>
shep-deploy deploy <sheep> --watch auto|manual
shep-deploy setup <sheep>
shep-deploy survey
shep-deploy on-remove

--watch changes the setting and returns without deploying. survey reports where every registered sheep stands and starts, registers and writes nothing.

Running as a dog

Adopted as a dog, shep-deploy takes no arguments and polls instead. Every 30 seconds by default, it deploys any watch = "auto" target whose branch has moved. Configure it in shep.toml:

[dog.deploy]
interval = "30s"
retention = 5
git_timeout = "5m"
build_timeout = "1h"
passthrough = ["CARGO_HOME"]

All five are read once, when the dog starts, so changing any takes a shep restart deploy.

retention is how many releases each target keeps besides the live one, so a target holds up to retention + 1 directories. The live release is spared unconditionally, whatever its age. It cannot be below 2: the release a failed deploy rolls back to is the second newest, so anything lower would silently disable rollback, and it is refused rather than clamped.

git_timeout bounds the fetch, which is the only git call that talks to a network. The rest operate on local directories and cannot hang on a remote. Targets are deployed one at a time, so without it a remote that drops packets rather than refusing them stops every target and every smit refresh, with no error and no log line. Five minutes by default, which is generous enough for a cold clone of a large repository.

build_timeout bounds the build command, against the same failure and for the same reason. A build that never finishes holds that same one-at-a-time loop, so no other target deploys and nothing is logged, because from the loop's point of view nothing has gone wrong. An hour by default, which no honest build should reach: it exists to turn a build that will never finish into an ordinary per-target failure, not to put a schedule on slow work. A build past it is killed as a process group, so whatever the build command started goes with it.

passthrough names environment variables a build may keep from the dog's own environment. See Security below for why that list starts empty.

One target's failure never stops the others, and never stops the dog. Each target's outcome is reported on its own and the loop carries on. up to date prints nothing at all, which is the answer to almost every tick of almost every target, and a line that repeats is said once rather than every interval.

A tick never begins while the previous one is still running, so a push landing during a build is deployed on the next tick rather than aborting the build in flight.

Nor does a second process. Each deploy takes an exclusive flock on its own tree for as long as it runs, so shep-deploy deploy web typed while the dog is mid-tick on web is refused in one sentence rather than colliding somewhere inside git. The lock is per sheep, so other targets are unaffected, and the kernel releases it if the holder dies, so a killed dog leaves nothing behind holding a sheep hostage.

Every tick also paints each target's smit, so shep flock shows which branch and sha it is on without a second command:

▲ main@a1b2c3      watched
⏸ main@f6e5d4      manual

Republished every tick rather than on change: shep holds a smit in memory only for as long as the connection that painted it stays open, so a dog that only published on change would show nothing at all after a daemon restart until its next deploy. A refused smit is logged and otherwise ignored, since it is cosmetic and never worth failing a deploy over.

A commit that fails is held

A commit that does not land is left alone until the branch moves. It is written into deploy.toml as failed, because otherwise the branch head and the deployed sha stay different and every tick runs the whole sequence again: fetch, full rebuild, swap, reload, wait out the verification budget, roll back, reload again. Two reloads of a live app and a build every thirty seconds, from one bad commit, until somebody notices.

Pushing a fix clears it, which is what CI does with a red commit; so does shep deploy <sheep>, which retries the same commit deliberately. The tradeoff is deliberate too: a deploy that failed on a network blip rather than on the commit waits for one of those two, rather than being retried on the next tick.

shep-deploy survey shows such a target as held, naming the commit it is holding, so a target stuck since yesterday does not read like one with nothing to do. Survey reads the record, never the remote, so a hold that a push already cleared still shows until the next tick.

Taking a sheep over

setup takes a sheep over: it builds the tree, fetches the repository, links the shared files in, builds the first release, and re-registers the sheep with its cwd set to current.

The first cutover is the one deploy that may have downtime. It runs two instances at once, so an app that does not bind with SO_REUSEPORT cannot take its own port while the original still holds it, and the new instance is then removed and the original left serving. Every deploy after the first replaces the instance rather than joining it, and does not meet this.

Most apps cannot set SO_REUSEPORT, and some cannot even be made to: Node refuses reusePort on macOS outright. For those, stop the sheep before the cutover and start it afterwards:

shep stop web

shep-deploy setup web

With the port free the newcomer binds and the cutover lands. It costs the downtime this section already warns about, and it is the difference between a setup that works and one that cannot. Measured 2026-08-28: the same app that failed the cutover while running completed it once stopped.

A cutover that was abandoned leaves the tree behind, and a sheep is not a deploy target until a cutover lands. shep-deploy deploy refuses such a target before anything at all happens, because its record names no deployed release.

That refusal is load-bearing rather than tidy. Without it the deploy would not stop: it would build, swap, reload the sheep at its own checkout, see a real turnover, and report success for a release nothing served.

Remove its tree and run setup again once the cause is fixed. Both setup and the failure message say this, and both print the resolved path to remove rather than a $SHEP_HOME you would have to expand yourself. setup leaves it watch = manual until the cutover lands, and --watch auto on one is refused for the same reason: it would ask for that deploy once every interval, unattended.

Verification

verify = "probed" (the default) needs the app to have a readiness_probe or wait_ready; without one, shep reports a process Online for not having died yet, so there is nothing to verify against and the deploy is refused. verify = "alive" is the deliberate downgrade: a new process, still running ten seconds later.

The first cutover is also the one deploy that is not verified against the readiness probe. shep reports a freshly started process Online once its listen_timeout elapses, whatever the probe said, and only aborts a reload whose replacement was not ready. So setup checks what it can: a new process started and was still the same process, not errored and not restarted, ten seconds later. A release that starts, stays up and serves nothing passes that. Every deploy after the first is verified against a new process reaching Online.

That used to be weaker than it sounds, and the gap was shep's rather than this crate's. Measured 2026-08-28 against a real shepherd: a sheep with an HTTP readiness_probe that never passes was marked Online about a second into a reload, well inside its listen_timeout, and stayed there. The cause was the reload's overlap. Both instances were up when the replacement's first probe landed, the outgoing one answered it, and shep took that as the incoming one proving itself. A release that started and never became ready was verified, recorded as deployed, and not rolled back, with the app down while the record said otherwise.

shep fixed it the same day. A probed app is now reloaded serially: the old instance drains first, so the only process that can answer the replacement's probe is the replacement. An app that sets reuse_port keeps the overlap it asks for and gets a second probe once the drained instance is gone. Either way a replacement that never answers is left starting rather than online, which is what this crate reads, so verify = "probed" now means what it says.

One thing to size correctly. A reuse_port app's reload costs one more listen_timeout than it used to, for that second probe, and the budget in deploy.rs is listen_timeout + graceful_timeout + slack per instance. For that one combination the budget can expire mid-check and roll back a release that was fine. A false rollback rather than a false success, which is the right direction to fail, but it wants a wider budget.

Rollback works for a release that crashes and for one that starts without serving. Both are caught.

Removing it

shep-deploy on-remove is the lifecycle hook: shep runs it before forgetting the dog, and it puts every sheep back where it ran before the dog took over. A sheep the dog bootstrapped has nowhere to go back to, so it is left running from current and the report says exactly that, with the path.

The deploy tree is never deleted. It is not the dog's to delete, and in the bootstrap case a running app is still pointing into it.

Exit codes

Follows shep's own taxonomy: 0 deployed or already up to date, 2 bad arguments, 4 bad configuration, 5 no daemon answered, 1 anything else.

Two are this dog's own:

code	means	the flock is
`12`	the deploy was rejected and the previous release was put back	healthy, on the old release
`13`	a first cutover landed and then could not tidy up	healthy, on the new release

A script that treats any nonzero code as "the deploy broke" will be wrong about both, because in each case the flock is serving.

Security

A deploy runs the build command from the repository being deployed. That is the point of it, and it is also the whole of the risk: bun install's postinstall scripts and make build are arbitrary code, chosen by whoever can land a commit on the branch you track.

That build runs as this process's uid unless the app sets user. Supervised as a dog, this process is the shepherd's child and shares its uid, and shep's own docs recommend running the shepherd as root so it can drop privileges per app. So the default arrangement is a repository's build script running as root, once per deploy.

Set user on the app and the build drops to that user's uid and primary group, with the shepherd's supplementary groups cleared, before it runs anything. A compromised build then gets that app's privileges and nothing more.

shep-deploy warns when it is about to run a build as root with no user set. It does not refuse. Whether an app runs without a user is shep's call and the operator's, not a deploy dog's.

A build starts from a cleared environment, not this process's. It gets PATH, HOME, LANG, LC_ALL and TZ, whatever passthrough names in [dog.deploy] in shep.toml, and the release's own [dog.deploy.build] env. Nothing else. Dropping uid and gid bounds what a build can touch; it does nothing about what it can read out of its own environment, because those values are copied in before the drop happens. A dog started with a registry token in its environment would otherwise hand it to every build it runs.

SSH_AUTH_SOCK is not in that base set, on purpose. A forwarded agent reaching a build lets the build authenticate as you anywhere that agent is trusted. Fetching happens in the dog's own process and keeps its own environment, so a private repository still clones; only the build loses the socket. Name it in passthrough if a build genuinely needs it.

build.artifacts may only name paths that really land inside the release or the dog's own build cache, resolved rather than spelled. A .., an absolute path, a committed symlink, or a CARGO_TARGET_DIR pointing elsewhere are all refused. That is narrower than it was: a build whose output genuinely lands outside both is no longer copyable, because the copy runs in the dog's own process at its own uid, and the [dog.deploy.build] block naming the path comes from the deployed repository rather than from you.

What the allowlist does not cover, and cannot. Your project's own secrets are not in the dog's environment, they are in your repository's working tree. A .env file is gitignored, which is exactly the rule that makes shep-deploy symlink it into every release, so the build reads it and so does the app at runtime. That is the intended behaviour and the reason shared files exist. It does mean a build command can read every secret the app itself can read, no matter what this allowlist says. The bound worth having there is user, so that a build and the app it builds are confined to the same one account.

Nothing else here handles credentials. Git auth is inherited from the user the dog runs as, so a private repository works as it does in that user's own shell, and no token passes through any URL or argument this crate builds.

Platform

Unix only. This is deliberate, not a gap waiting to be filled by accident: the deploy model is rename(2) over a symlink, the build's privilege drop is a uid and a gid, and both are Unix concepts the code uses directly rather than through a portability layer. Building on Windows fails with one sentence saying so. Windows support is planned and will be scoped on its own.

Status

Working: the deploy sequence, the operator commands, opt-in, the poll loop, retention, and restore on removal. Tested against a real shepherd.

Not built: Windows.

See docs/writing-plans/plans/2026-08-26-deploy-engine.md for what was built, and the design spec for what it is for.

License

MIT OR Apache-2.0, at your option.

shep-deploy 0.2.0