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  7. Variable Registry (var/var_or)

Variable Registry (var/var_or)

Variable Registry

The variable registry resolves configuration values from CLOACINA_VAR_ environment variables at runtime, keeping secrets and environment-specific settings out of your workflow code.

Prerequisites

  • A working workflow (Rust or Python)

Convention

All variables use the CLOACINA_VAR_ prefix:

export CLOACINA_VAR_KAFKA_BROKER=localhost:9092
export CLOACINA_VAR_ANALYTICS_DB=postgres://user:pass@host/db
export CLOACINA_VAR_API_KEY=abc123
export CLOACINA_VAR_MODEL_THRESHOLD=0.85

In your code, you reference the name without the prefix.

Rust API

Required Variable 

use cloacina::var;

// Reads CLOACINA_VAR_KAFKA_BROKER
let broker = var("KAFKA_BROKER")?;
// Returns Err(VarNotFound) if not set

Optional Variable with Default 

use cloacina::var_or;

// Reads CLOACINA_VAR_MODEL_THRESHOLD, falls back to "0.5"
let threshold: f64 = var_or("MODEL_THRESHOLD", "0.5").parse().unwrap();

Template Resolution

Expand {{ VAR_NAME }} placeholders in configuration strings:

use cloacina::var::resolve_template;

// With CLOACINA_VAR_HOST=db.example.com and CLOACINA_VAR_PORT=5432
let url = resolve_template("postgres://user@{{ HOST }}:{{ PORT }}/mydb")?;
// Result: "postgres://user@db.example.com:5432/mydb"

If any referenced variables are missing, resolve_template returns Err(Vec<VarNotFound>) listing all unresolved names. Unresolved placeholders are preserved literally in the output. Unclosed {{ without a matching }} is copied through unchanged (no error).

Python API

Required Variable 

import cloaca

# Reads CLOACINA_VAR_KAFKA_BROKER
broker = cloaca.var("KAFKA_BROKER")
# Raises KeyError if not set

Optional Variable with Default 

# Reads CLOACINA_VAR_MODEL_THRESHOLD, falls back to "0.5"
threshold = float(cloaca.var_or("MODEL_THRESHOLD", "0.5"))

Use Cases

Per-Environment Database Connections 

@cloaca.task(id="load_data")
def load_data(context):
    db_url = cloaca.var("WAREHOUSE_URL")
    # dev:  CLOACINA_VAR_WAREHOUSE_URL=sqlite:///tmp/dev.db
    # prod: CLOACINA_VAR_WAREHOUSE_URL=postgres://prod-host/warehouse
    conn = connect(db_url)
    conn.execute(...)
    return context

Per-Tenant Credentials 

@cloaca.task(id="call_api")
def call_api(context):
    api_key = cloaca.var("PARTNER_API_KEY")
    # Each tenant's daemon sets a different key
    response = requests.get(url, headers={"X-API-Key": api_key})
    context.set("response", response.json())
    return context

Configuration Thresholds 

#[task(id = "evaluate_model")]
async fn evaluate(context: &mut Context<serde_json::Value>) -> Result<(), TaskError> {
    let threshold: f64 = var_or("CONFIDENCE_THRESHOLD", "0.8")
        .parse()
        .map_err(|e| TaskError::execution(format!("bad threshold: {e}")))?;

    let score = context.get("score").unwrap().as_f64().unwrap();
    context.insert("passed", serde_json::json!(score >= threshold))?;
    Ok(())
}

Template Strings in Configuration

Configuration strings can reference variables with {{ VAR_NAME }} syntax. This is expanded at load time using resolve_template() against the host’s environment variables:

let config = resolve_template("broker={{ KAFKA_BROKER }}:{{ KAFKA_PORT }}")?;
// With CLOACINA_VAR_KAFKA_BROKER=localhost and CLOACINA_VAR_KAFKA_PORT=9092
// Result: "broker=localhost:9092"

Whitespace inside {{ }} is trimmed — {{ HOST }} resolves the same as {{ HOST }}. There is no escape syntax; {{ is always treated as a variable reference.

Error Handling

Rust

var() returns Result<String, VarNotFound>. The error message includes the expected environment variable name:

required variable 'KAFKA_BROKER' not set (expected env var CLOACINA_VAR_KAFKA_BROKER)

Python

cloaca.var() raises KeyError with a message like:

KeyError: "CLOACINA_VAR_KAFKA_BROKER not set"

Use cloaca.var_or() if the value is truly optional.

See Also

gdoc_arrow_left_alt Monitoring Executions Cleaning Up Events gdoc_arrow_right_alt