System.CircuitBreaker

This is a batteries mostly-included circuit breaker library. It provides automatic backoff behavior by preventing calls to a failing resource. For example, if a particular service is currently overloaded and begins failing to respond to requests, then the circuit breaker will detect those errors and prevent further calls from actually hitting the server in question. Once the service has had a chance to stabilize the circuit breaker will allow a "testing" call to pass through. If it succeeds, then all other calls are allowed to flow through. If it fails then it waits a bit longer before testing again.

Documentation

data CircuitBreaker (label :: Symbol) (dripFreq :: Nat) (errorThreshold :: Nat)

The definition of a particular circuit breaker

newtype CircuitBreakerConf

Constructors

CBConf

Fields

• cbBreakers :: MVar (HashMap Text (MVar CircuitState))

Instances

HasCircuitConf CircuitBreakerConf

Defined in System.CircuitBreaker

Methods

getCircuitState :: CircuitBreakerConf -> CircuitBreakerConf

withBreaker :: (KnownSymbol label, KnownNat df, KnownNat et, Monad m, MonadUnliftIO m, MonadReader env m, HasCircuitConf env) => CircuitBreaker label df et -> m a -> m (Either CircutBreakerError a)

Brackets a computation with short-circuit logic. If an uncaught error occurs, then the circuit breaker opens, which causes all additional threads entering the wrapped code to fail until the specified timeout has expired. Once the timeout expires, a single thread may enter the protected region. If the call succeeds, then the circuit breaker allows all other traffic through. Otherwise, it resets the timeout, after which the above algorithm repeats.

Important Note: This does not catch errors. If an IO error is thrown, it will bubble up from this function. Internally, if the breaker is tripped, it will prevent further calls

data CircutBreakerError

Constructors

Failed

CircuitBreakerClosed Text

Instances

Eq CircutBreakerError

Defined in System.CircuitBreaker

Methods

(==) :: CircutBreakerError -> CircutBreakerError -> Bool

(/=) :: CircutBreakerError -> CircutBreakerError -> Bool

Ord CircutBreakerError

Defined in System.CircuitBreaker

Methods

compare :: CircutBreakerError -> CircutBreakerError -> Ordering

(<) :: CircutBreakerError -> CircutBreakerError -> Bool

(<=) :: CircutBreakerError -> CircutBreakerError -> Bool

(>) :: CircutBreakerError -> CircutBreakerError -> Bool

(>=) :: CircutBreakerError -> CircutBreakerError -> Bool

max :: CircutBreakerError -> CircutBreakerError -> CircutBreakerError

min :: CircutBreakerError -> CircutBreakerError -> CircutBreakerError

Show CircutBreakerError

Defined in System.CircuitBreaker

Methods

showsPrec :: Int -> CircutBreakerError -> ShowS

show :: CircutBreakerError -> String

showList :: [CircutBreakerError] -> ShowS

class HasCircuitConf env where

A constraint that allows pullng the circuit breaker

Methods

getCircuitState :: env -> CircuitBreakerConf

Instances

HasCircuitConf CircuitBreakerConf

Defined in System.CircuitBreaker

Methods

getCircuitState :: CircuitBreakerConf -> CircuitBreakerConf

data CircuitState

Constructors

CircuitState

Fields

• errorCount :: Natural
• currentState :: !CBCondition

Instances

Show CircuitState

Defined in System.CircuitBreaker

Methods

showsPrec :: Int -> CircuitState -> ShowS

show :: CircuitState -> String

showList :: [CircuitState] -> ShowS

data CircuitAction

Constructors

SkipClosed

Run

Instances

Eq CircuitAction

Defined in System.CircuitBreaker

Methods

(==) :: CircuitAction -> CircuitAction -> Bool

(/=) :: CircuitAction -> CircuitAction -> Bool

Show CircuitAction

Defined in System.CircuitBreaker

Methods

showsPrec :: Int -> CircuitAction -> ShowS

show :: CircuitAction -> String

showList :: [CircuitAction] -> ShowS

newtype ErrorThreshold

Constructors

ET Natural

data CBCondition

The current condition of a CircutBreaker may be Active, Testing, or Waiting for the timeout to elapse.

Constructors

Active

Testing

Waiting

Instances

Bounded CBCondition

Defined in System.CircuitBreaker

Methods

minBound :: CBCondition

maxBound :: CBCondition

Enum CBCondition

Defined in System.CircuitBreaker

Methods

succ :: CBCondition -> CBCondition

pred :: CBCondition -> CBCondition

toEnum :: Int -> CBCondition

fromEnum :: CBCondition -> Int

enumFrom :: CBCondition -> [CBCondition]

enumFromThen :: CBCondition -> CBCondition -> [CBCondition]

enumFromTo :: CBCondition -> CBCondition -> [CBCondition]

enumFromThenTo :: CBCondition -> CBCondition -> CBCondition -> [CBCondition]

Eq CBCondition

Defined in System.CircuitBreaker

Methods

(==) :: CBCondition -> CBCondition -> Bool

(/=) :: CBCondition -> CBCondition -> Bool

Ord CBCondition

Defined in System.CircuitBreaker

Methods

compare :: CBCondition -> CBCondition -> Ordering

(<) :: CBCondition -> CBCondition -> Bool

(<=) :: CBCondition -> CBCondition -> Bool

(>) :: CBCondition -> CBCondition -> Bool

(>=) :: CBCondition -> CBCondition -> Bool

max :: CBCondition -> CBCondition -> CBCondition

min :: CBCondition -> CBCondition -> CBCondition

Show CBCondition

Defined in System.CircuitBreaker

Methods

showsPrec :: Int -> CBCondition -> ShowS

show :: CBCondition -> String

showList :: [CBCondition] -> ShowS

initialBreakerState :: MonadUnliftIO m => m CircuitBreakerConf

Initialize the storage for the process' circuit breakers

Exported for testing

breakerTransitionGuard :: MonadUnliftIO m => MVar CircuitState -> ErrorThreshold -> m CircuitAction

Given the current state of the circuit breaker, determine what action should be taken during the body of the bracket.

Condition rules: 1) If the circuit breaker is in Active then pass the call on 2) If the circuit breaker is in Testing then fail the call 3) If the circuit breaker is in Waiting and the timeout has not elapsed then fail the call 4) If the circuit breaker is in Waiting and the timeout has elapsed then convert to Testing and try the call

breakerTryPerformAction

Arguments

:: MonadUnliftIO m

=> Text

label

-> m a

Action to perform

-> MVar CircuitState

Pointer to the breaker state

-> CircuitAction

-> m (Either CircutBreakerError a)

Conditionally performs an action with in a circuit breaker, as determined by the current breaker state.

decrementErrorCount :: MonadUnliftIO m => MVar CircuitState -> m ()

Decrements a counter