Activities

Activities are functions that execute non-deterministic operations. Any function.lua or process.lua entry can be registered as a Temporal activity by adding metadata.

Registering Activities

Add meta.temporal.activity to register a function as an activity:

- name: charge_payment
  kind: function.lua
  source: file://payment.lua
  method: charge
  modules:
    - http_client
    - json
  meta:
    temporal:
      activity:
        worker: app:worker

Metadata Fields

Implementation

Activities are regular Lua functions:

-- payment.lua
local http = require("http_client")
local json = require("json")

local function charge(input)
    local response, err = http.post("https://api.stripe.com/v1/charges", {
        headers = {
            ["Authorization"] = "Bearer " .. input.api_key,
            ["Content-Type"] = "application/json"
        },
        body = json.encode({
            amount = input.amount,
            currency = input.currency,
            source = input.token
        })
    })

    if err then
        return nil, err
    end

    return json.decode(response:body())
end

return { charge = charge }

Calling Activities

From workflows, use the funcs module:

local funcs = require("funcs")

local result, err = funcs.call("app:charge_payment", {
    amount = 5000,
    currency = "usd",
    token = "tok_visa",
    api_key = ctx.stripe_key
})

if err then
    return nil, err
end

Activity Options

Configure timeouts, retry behavior, and other execution parameters using the executor builder:

local funcs = require("funcs")

local executor = funcs.new():with_options({
    ["activity.start_to_close_timeout"] = "30s",
    ["activity.schedule_to_close_timeout"] = "5m",
    ["activity.heartbeat_timeout"] = "10s",
    ["activity.retry_policy"] = {
        maximum_attempts = 3,
        initial_interval = 1000,
        backoff_coefficient = 2.0,
        maximum_interval = 60000,
    }
})

local result, err = executor:call("app:charge_payment", input)

The executor is immutable and reusable. Build it once and use it for multiple calls:

local reliable = funcs.new():with_options({
    ["activity.start_to_close_timeout"] = "60s",
    ["activity.retry_policy"] = {
        maximum_attempts = 5,
        initial_interval = 2000,
        backoff_coefficient = 2.0,
        maximum_interval = 120000,
    }
})

local a, err = reliable:call("app:step_one", input)
local b, err = reliable:call("app:step_two", a)

Options Reference

Duration values accept strings ("5s", "10m", "1h") or milliseconds as numbers.

Retry Policy

Configure automatic retry behavior for failed activities:

["activity.retry_policy"] = {
    initial_interval = 1000,         -- ms before first retry
    backoff_coefficient = 2.0,       -- multiplier for each retry
    maximum_interval = 300000,       -- max interval between retries (ms)
    maximum_attempts = 10,           -- max retry attempts (0 = unlimited)
    non_retryable_error_types = {    -- errors that skip retries
        "INVALID",
        "PERMISSION_DENIED"
    }
}

Timeout Relationships

|--- schedule_to_close_timeout --------------------------------|
|--- schedule_to_start_timeout ---|--- start_to_close_timeout -|
     (waiting in queue)                (executing)

• start_to_close_timeout: How long the activity itself can run. This is the most commonly used timeout.
• schedule_to_close_timeout: Total time from when the activity is scheduled until it completes, including queue wait time and retries.
• schedule_to_start_timeout: Max time the activity can wait in the task queue before a worker picks it up.
• heartbeat_timeout: For long-running activities, the max time between heartbeat reports.

Local Activities

Local activities execute in the workflow worker process without separate task queue polling:

- name: validate_input
  kind: function.lua
  source: file://validate.lua
  method: validate
  modules:
    - json
  meta:
    temporal:
      activity:
        worker: app:worker
        local: true

Characteristics:

• Execute in workflow worker process
• Lower latency (no task queue roundtrip)
• No separate task queue overhead
• Limited to short execution times
• No heartbeating

Use local activities for fast, short operations like input validation, data transformation, or cache lookups.

Activity Naming

Activities are registered with their full entry ID as the name:

namespace: app
entries:
  - name: charge_payment
    kind: function.lua
    # ...

Activity name: app:charge_payment

Context Propagation

Context values set when spawning the workflow are available inside activities:

-- Spawner sets context
local spawner = process.with_context({
    user_id = "user-1",
    tenant = "tenant-1",
})
local pid = spawner:spawn("app:order_workflow", "app:worker", order)

-- Activity reads context
local ctx = require("ctx")

local function process_order(input)
    local user_id = ctx.get("user_id")   -- "user-1"
    local tenant = ctx.get("tenant")     -- "tenant-1"
    -- use context for authorization, logging, etc.
end

Activities called from a workflow with funcs.new():with_context() also propagate context:

-- Inside workflow
local executor = funcs.new():with_context({trace_id = "abc-123"})
local result, err = executor:call("app:charge_payment", input)

Error Handling

Return errors via the standard Lua pattern:

local errors = require("errors")

local function charge(input)
    if not input.amount or input.amount <= 0 then
        return nil, errors.new("INVALID", "amount must be positive")
    end

    local response, err = http.post(url, options)
    if err then
        return nil, errors.wrap(err, "payment API failed")
    end

    if response:status() >= 400 then
        return nil, errors.new("FAILED", "payment declined")
    end

    return json.decode(response:body())
end

Error Objects

Activity errors propagated to workflows carry structured metadata:

local result, err = funcs.call("app:charge_payment", input)
if err then
    err:kind()       -- error classification string
    err:retryable()  -- boolean, whether retry makes sense
    err:message()    -- human-readable error message
end

Failure Modes

local executor = funcs.new():with_options({
    ["activity.retry_policy"] = {maximum_attempts = 1}
})

local result, err = executor:call("app:missing_activity", input)
if err then
    print(err:kind())      -- "NOT_FOUND"
    print(err:retryable())  -- false
end

Process Activities

process.lua entries can also be registered as activities for long-running operations:

- name: long_task
  kind: process.lua
  source: file://long_task.lua
  method: main
  modules:
    - http_client
  meta:
    temporal:
      activity:
        worker: app:worker

See Also

• Overview - Configuration
• Workflows - Workflow implementation
• Functions - Function module
• Error Handling - Error types and patterns