Solti SDK

Build task-execution agents from Kubernetes-shaped resources, pluggable runners, and optional HTTP or gRPC boundaries.

Solti is a modular Rust SDK. It provides the resource model, routing, reconciliation, execution backends, APIs, discovery, TLS, logging, and metrics used by an agent binary.

Your binary selects the required crates or enables them through the solti umbrella crate. Your binary still owns configuration, deployment, and the final security boundary.

Solti uses Taskvisor for supervised attempt lifecycles.

| Quick start | Architecture | Platform limits | Examples |

The stack you stop wiring

A task agent needs more than process spawning. It must validate desired state, select a runtime, reconcile changes, supervise attempts, expose status, and shut down cleanly.

Solti separates those responsibilities:

Concern	SDK boundary
Resource contract	Kubernetes-shaped Task, metadata, spec, status, and watches
Workload selection	GVK routing plus optional runner label selectors
Desired state	Asynchronous latest-wins reconciliation
Attempt lifecycle	Taskvisor restart, timeout, cancellation, and admission
Execution	Subprocess, native containerd 2.x, or application-owned runner
Public API	HTTP/JSON or gRPC
Agent registration	Outbound HTTP or gRPC discovery
Operations	TLS, logging, Prometheus, and live output

Each layer has a direct crate. The umbrella crate only forwards features and namespaces.

Check the fit first

Use Solti when a binary needs versioned Task resources, pluggable workload kinds, desired-state reconciliation, or a public agent API.

If the process only needs to supervise ordinary async functions, use Taskvisor directly. It has a smaller API and no resource or network layer.

Solti is not a durable job system or a control plane. Core state and live output are process-local. A compatible control plane, persistent storage, authorization policy, and deployment topology remain separate concerns.

Quick start

Add the umbrella crate with only the required capabilities:

[dependencies]
solti = { version = "0.0.4", features = ["core", "exec-subprocess"] }
tokio = { version = "1", features = ["macros", "rt", "time"] }

Put this in src/main.rs, then run cargo run. The parent registers a subprocess runner and supervises one execution of the same binary.

use std::{env, io, time::Duration};

use solti::{
    core::SupervisorApi,
    exec::subprocess::register_subprocess_runner,
    model::{
        Flag, RestartPolicy, SubprocessMode, SubprocessSpec, TaskEnv, TaskManifest, TaskSpec,
        TaskWorkload,
    },
    runner::RunnerRouter,
};

const CHILD_MODE: &str = "--solti-quick-start-child";

#[tokio::main(flavor = "current_thread")]
async fn main() -> Result<(), Box<dyn std::error::Error>> {
    if env::args().nth(1).as_deref() == Some(CHILD_MODE) {
        println!("hello from the supervised subprocess");
        return Ok(());
    }

    let mut router = RunnerRouter::new();
    register_subprocess_runner(&mut router, "default")?;
    let supervisor = SupervisorApi::builder(router).start().await?;

    let command = env::current_exe()?.to_string_lossy().into_owned();
    let workload = TaskWorkload::Subprocess(SubprocessSpec::new(
        SubprocessMode::Command {
            command,
            args: vec![CHILD_MODE.into()],
        },
        TaskEnv::new(),
        None,
        Flag::enabled(),
    ));
    let spec = TaskSpec::builder("quick-start", workload, 30_000_u64)
        .restart(RestartPolicy::Never)
        .build()?;
    let committed = supervisor
        .create_task(TaskManifest::new("quick-start", spec)?)
        .await?;
    let name = committed.name().clone();
    println!("committed {name}");

    let phase = tokio::time::timeout(Duration::from_secs(35), async {
        loop {
            let task = supervisor
                .get_task(&name)
                .ok_or_else(|| io::Error::other("task disappeared"))?;
            let phase = task.status().phase();
            if phase.is_terminal() {
                break Ok::<_, io::Error>(phase);
            }
            tokio::time::sleep(Duration::from_millis(25)).await;
        }
    })
    .await??;

    println!("finished {name}: {phase}");
    supervisor.shutdown().await?;
    Ok(())
}

create_task returns after desired state is committed. Reconciliation and execution continue asynchronously.

The complete lifecycle with live output and history is in task_subprocess.rs.

Build only what you need

All solti features are disabled by default. Higher-level features enable their required lower layers.

Binary requirement	Start with
Resource types and JSON Schema	model
Custom runner registration	runner
Conditional sequential workloads	chain
In-process desired-state runtime	core
Subprocess task runtime	core, exec-subprocess
Native containerd task runtime	core, exec-containerd
HTTP Task API	api-core-adapter, api-http, exec-subprocess
gRPC Task API	api-core-adapter, api-grpc, exec-subprocess
gRPC Task API with TLS or mTLS	api-core-adapter, api-grpc-tls, exec-subprocess
HTTP agent with discovery	api-core-adapter, api-http, discover-http, exec-subprocess
Complete standard integration set	full

exec-containerd is a native containerd 2.x adapter. It is not a Docker, CRI, or Docker Compose integration.

Architecture

The component graph is acyclic. Arrows in the diagram point toward the dependency or runtime contract being consumed.

solti-core never depends on solti-exec. Execution backends implement the solti-runner contract and are registered by the binary.

solti-api depends on core only through core-adapter. Its handler and transport boundaries can be used with another implementation.

solti-discover is an outbound client. It does not run the agent API or depend on core.

solti-tls has no SDK dependencies. solti-prometheus connects to producers only through feature-selected adapters.

Crates

Crate	Owns
solti	Umbrella feature forwarding and canonical namespaces
solti-model	Resources, workloads, policies, selectors, capabilities, and tokens
solti-runner	Runner contract, GVK routing, selectors, and execution context
solti-chain	Conditional sequential composition of nested workloads
solti-core	Desired state, reconciliation, watches, history, and live output
solti-exec	Execution backends and host-process controls
solti-api	HTTP/JSON and gRPC Task APIs
solti-discover	Agent registration and heartbeat client
solti-tls	TLS and mTLS identities, trust roots, and rustls configuration
solti-observe	Structured logging and supervised timezone refresh
solti-prometheus	Metrics adapters, collectors, and exporter endpoint

Depend on one component crate when one boundary is enough. Use solti when a binary composes several components.

Task resources

Solti follows Kubernetes resource conventions. A Task has apiVersion, kind, metadata, spec, and status.

The caller owns desired fields. Core owns UID, resource version, generation, timestamps, status, and conditions.

Built-in workload kinds are Subprocess, Container, Wasm, and Embedded. Wasm is a model contract; this repository does not provide a built-in WASM runner.

Application-owned workload kinds use ExtensionWorkload with a non-solti.io GVK and strict runner-side decoding. Runner routing uses workload GVK and an optional Kubernetes-style label selector.

Embedded carries an in-process TaskRef supplied by the binary. It bypasses runner routing and has no HTTP or gRPC representation.

Conditional chains

The optional solti-chain runner represents a Chain as one ordinary Task. Its steps are nested workloads, and exactly one step is active at a time. Each successful or failed step may select one next step.

Chain uses a regular extension workload under Task.spec.workload. Existing HTTP and gRPC Task operations carry it without a new resource API.

The outer Task owns timeout, restart, backoff, admission, cancellation, status, history, and output. Steps are not child Task resources and do not have independent lifecycle policies. Restarting the outer Task starts the chain again from its entry step.

Reconciliation and execution

Create and apply commit desired state before runtime work begins. The resource status reports the observed result through phase, generation, attempt, and the Reconciled condition.

Reconciliation is latest-wins. An older generation is discarded before expensive runner construction when a newer generation is already committed.

There is no staged rollout or availability guarantee. In-flight side effects may finish before the next reconciliation compensates for them.

Core does not run an infinite reconciliation retry queue. Applying an identical manifest schedules one manual retry only when Reconciled=False.

Taskvisor owns attempt restart, backoff, timeout, admission, and cancellation. Core retains bounded TaskRun history separately from the current Task status.

Public Task API

solti-api exposes the same task operations over HTTP/JSON and gRPC:

Operation	Result
Create	Commit a new named Task
Apply	Create or update desired state
Get	Read one Task
List	Filter and paginate a stable collection snapshot
Watch	Stream retained changes and then live changes
Run history	Read retained attempts
Logs	Stream live stdout and stderr
Delete	Stop the runtime and remove the Task and its history

HTTP uses the fixed root /apis/solti.io/v1 in the current solti-api release. HttpApi::build returns the router and its generated OpenAPI 3.1 document.

gRPC uses the solti.task.v1 protobuf package. Generated server and client types are available from the crate.

Each SDK binary serves the API version compiled into its selected solti-api version. A control plane that manages different binary generations must route each advertised version to its matching contract.

Bearer authentication is disabled until the binary calls with_auth or with_authenticator. An optional with_authorizer policy runs before each validated Task API operation. The HTTP and gRPC boundaries enforce a 4 MiB request or message limit.

Read the complete route, message, pagination, watch, and error contract in solti-api/CONTRACT.md.

Discovery

solti-discover advertises one agent endpoint, API version, runner capabilities, identity, and uptime to a control plane.

The discovery loop is returned as an Embedded manifest and TaskRef. The binary decides whether to submit it to core.

HTTP and gRPC transports are independent features. Retryable transport failures use the generated task's Taskvisor policy. Permanent configuration or authentication failures stop the task.

Discovery does not expose an inbound server. It does not persist registration state.

Read the versioned wire contract in solti-discover/CONTRACT.md.

Authentication and TLS

solti-model::Token is a redacted bearer secret with constant-time comparison. solti-api can verify it on every route and RPC. solti-discover can send it with every heartbeat.

The static token is authentication only. solti-api also exposes application hooks for bearer authentication and operation-level authorization. The SDK does not provide users, tenants, RBAC rules, tenant filtering, policy storage, secret rotation, or secret persistence.

solti-tls separates server identity, client identity, and trust roots. It supports TLS and mandatory client-certificate authentication.

api-grpc-tls converts the shared server configuration for tonic. HTTP server TLS is owned by the server that hosts the axum router. discover-tls applies custom roots or mTLS to outbound HTTPS connections.

Bearer authentication and TLS are independent.

Execution backends and platform limits

Native containerd execution is Linux-only. macOS can build the adapter and inspect its configuration, but it cannot start a native container attempt.

Runtime path	Current platform contract	Isolation boundary
Embedded	Application's supported Tokio targets	Same process; no operating-system isolation
Subprocess	Linux and macOS	Child process; Unix session and process group
Non-Unix subprocess path	Implementation exists; Windows is not currently supported	Child process only
Custom container engine	Defined by the application adapter	Defined by that engine
Native containerd 2.x	Linux host and Linux container images	OCI runtime plus containerd task lifecycle

Host-process controls

The subprocess path always validates configuration before runner registration. Configured controls fail closed when the current platform cannot enforce them.

Control	Platform
Session, process group, signal reset, umask	Unix
RLIMIT_NOFILE, RLIMIT_FSIZE, core dumps	Unix
Pinned working directory	Unix
Explicit descriptor passlist	Linux
Descriptor snapshot and close-on-exec checks	Other Unix
cgroup v2 CPU, memory, and process limits	Linux
Mount, network, IPC, UTS, and cgroup namespaces	Linux
UID, GID, supplementary groups, capabilities	Linux
no_new_privs and seccomp denylist	Linux

The default subprocess backend does not enable optional resource or security controls. It clears the inherited environment, pins the working directory on Unix, restricts descriptor inheritance, and owns child cleanup.

These controls harden a host process. They do not form a complete sandbox for untrusted code.

Native containerd 2.x

The built-in adapter connects to one explicit Unix socket and namespace. It does not start or discover containerd.

It requires:

• a Linux host;
• containerd major version 2;
• configured snapshotter and OCI runtime plugins;
• a cached or reachable Linux image;
• an I/O root visible at the same path to the SDK process and containerd;
• protoc during builds that compile containerd-client bindings.

Network mode is either none or host. none creates an OCI network namespace without configuring interfaces. host shares the host network namespace.

The adapter does not provide bridge networking, CNI, CRI, port publishing, volumes, or Docker Compose semantics. The final binary must add those layers if its product requires them.

Run task_containerd.rs on a prepared Linux host. On other platforms the example prints the prerequisite and exits without contacting a daemon.

State, output, and production limits

Keep these boundaries explicit:

• Core stores Tasks, runs, watch history, and runtime bindings in memory.
• Process restart loses all core state.
• Live output is bounded and lossy.
• Core does not persist or replay output by itself.
• Optional core hooks can forward task, run, and output events to an application-owned store.
• A slow output subscriber receives Lagged after events are dropped.
• Watch history is bounded by change count and serialized Task bytes.
• A watch can resume only while its resource version remains retained.
• Snapshot pagination is consistent only while its continuation remains valid.
• Reconciliation is latest-wins and has no staged availability guarantee.
• Discovery registration state is not persisted.
• Static bearer authentication alone does not provide authorization or tenant isolation.
• Host-process controls are hardening, not a complete untrusted-code sandbox.
• The native container adapter provides no CRI or CNI implementation.
• The SDK contains no durable log sink.
• The SDK contains no control-plane server.

Use the persistence hooks with an external store when tasks or logs must survive process termination. The application owns delivery retries and its restart recovery flow. The SDK does not load persisted state at startup. Install application authorization and sandbox policy at the binary or service boundary.

Feature flags

All umbrella features are off by default.

Feature or family	Adds
model	solti-model with JSON Schema support
runner	Runner contract, model, and Taskvisor
core	Desired-state supervisor and Taskvisor controller
exec	Base solti-exec namespace
exec-host-process	Low-level host-process policy
exec-subprocess	Subprocess runner and required lower layers
exec-container	Engine-neutral container runner
exec-containerd	Native containerd 2.x adapter
exec-seccomp	Linux host-process seccomp renderer
api	API handler and model boundary
api-http, api-grpc	HTTP or gRPC transport
api-core-adapter	Adapter from the API handler to SupervisorApi
api-grpc-tls	Shared TLS conversion for tonic
discover	Base discovery contracts
discover-http, discover-grpc	Outbound discovery transport
discover-tls	Custom roots or mTLS for discovery
observe	Logging configuration
observe-*	Journald, log compatibility, or timezone refresh
prometheus-base	Prometheus namespace and base contracts
prometheus	Runner and Taskvisor-controller metrics bundle
prometheus-*	API, discovery, process, server, state, runner, or Taskvisor adapters
prometheus-full	Every Prometheus adapter
taskvisor-*	Forwarded Taskvisor integrations
tls	Shared TLS and mTLS types
full	Complete standard integration set

exec-seccomp provides the filter implementation. Combine it with exec-subprocess to apply the filter to subprocess attempts.

api-http and api-grpc do not enable core. Add api-core-adapter when the public API delegates to SupervisorApi.

full compiles the native containerd adapter. Container execution remains Linux-only.

Examples

From a cloned checkout, start with the direct Task lifecycle:

cargo run -p solti --example task_subprocess \
  --features core,exec-subprocess

Names identify the boundary:

• task_* calls the in-process Task lifecycle directly;
• agent_* assembles an API or discovery boundary;
• operations_* composes metrics, logging, and maintenance.

Task lifecycle

Example	Features	Result
task_chain.rs	chain,core,exec-subprocess	Conditional steps with failure recovery
task_subprocess.rs	core,exec-subprocess	Output, reconciliation, terminal status, and history
task_custom_workload.rs	core	Application-owned TcpProbe GVK and runner
task_containerd.rs	core,exec-containerd	Native containerd 2.x attempt; Linux runtime required

Agent boundaries

Example	Features	Result
agent_http.rs	api-core-adapter,api-http,exec-subprocess	HTTP Task API, OpenAPI, and runnable curl calls
agent_grpc.rs	api-core-adapter,api-grpc,exec-subprocess	gRPC Task API, bearer auth, and grpcurl calls
agent_grpc_mtls.rs	api-core-adapter,api-grpc-tls,exec-subprocess	Anonymous rejection and authenticated mTLS client
agent_http_discovery.rs	api-core-adapter,api-http,discover-http,exec-subprocess	Inbound Task API and outbound discovery heartbeat

Operations

Example	Features	Result
operations_prometheus.rs	core,exec-subprocess,prometheus,prometheus-server,prometheus-state	Supervised /metrics with real runtime samples
operations_observe.rs	core,exec-subprocess,observe-timezone-sync	Logging and supervised timezone maintenance

agent_http and agent_grpc remain active until Ctrl-C. They print commands that can be run from a second terminal.

operations_prometheus serves http://127.0.0.1:9090/metrics until Ctrl-C. Set SOLTI_METRICS_ADDR to use another listen address.

task_containerd requires Linux and an accessible containerd 2.x daemon for a real attempt.

Development

Vendor the pinned protobuf contracts after a fresh checkout:

task proto/vendor

The task fetches the revision pinned in Taskfile.yml. Generated protobuf trees are ignored by Git and included in published transport crates.

Run the workspace checks:

task ci/fmt
task ci/clippy
task ci/test
task ci/docs
task ci/publish-dry-run

The release order is declared in .github/crates.txt. Component crates are published before the solti umbrella crate.

Contributing

Issues and pull requests are welcome. Start with the relevant crate README.

Read the architecture guides before changing the model, core, or execution boundaries. Read the Task API contract or discovery contract before changing wire behavior.

Read the contributing guide before a large change.

If Solti helps your project, a GitHub star helps other Rust developers find it.