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050-low-level-architecture.md

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Low-level Architecture
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diego-release
locket

Low-level Architecture

Locket is a grpc server. golang clients can communicate with the Locket service using LocketClient. Clients in other languages can use the .proto files to generate a client.

Ifrit Runners

Ifrit is a simple process model for composing single-purpose units of work into larger programs.

Locket lock runner

Th LockRunner can be used to acquire a lock. Note the runner will not be ready until the lock is acquired but will exit as soon as the lock is lost.

Locket presence runner

The PresenceRunner can be used to register the service presence. The only difference between a presence runner and lock runner is the presence runner will not exit when the lock is lost. Instead, it will retry to acquire the lock in the background.

RPC Calls

Ifrit runners are the most convenient way to use the locket service. For more advanced use cases please refer to the RPC calls documented below

LockRequest

Lock request is used to acquire a lock. A lock can be held by one owner only. It is not an error to acquire the lock more than once. In fact, this is required as explained below, otherwise the lock will expire. A LockRequest is composed of the following fields:

  1. TtlInSeconds the ttl of the lock in seconds. must be greather than 0. the client is required to acquire the lock again before the TTL elapses, otherwise the lock will be released
  2. Resource [required] a resource defines the lock and is composed of the following fields:
    1. Key [required] the name of the lock. this can be any arbitrary name
    2. Owner [required] a unique identifier of the owner. A claimed lock can only be acquired by the same owner. Other owners will get an error
    3. Value [optional] Arbitrary metadata that can be stored with the lock
    4. TypeCode [optional] an enum integer value that can be later used to fetch all locks by type. The TypeCode enum currently specifies UNKNOWN (0), LOCK (1) and PRESENCE (2).
    5. Type [deprecated; optional] a value that can be later used to fetch all locks by type. Diego currently uses "lock" and "presence". Type will go away in favor of TypeCode in the next major release of Diego.

Returns a LockResponse

The following errors can be returned:

  1. ErrLockCollision if the lock is already acquired by a different owner
  2. ErrInvalidTTL if the ttl is invalid
  3. ErrInvalidOwner if the owner is empty

Note other unstructured errors can be returned from the client. For example, a grpc error will returned if the client is having trouble talking to the server. Also, sql errors could be returned.

LockResponse

The lock response is currently empty. The client will have to use the returned error to determine if the lock was successfully acquired.

ReleaseRequest

Release a previously acquired lock. A ReleaseRequest is composed of the following fields:

  1. Resource [required] a resource defines the lock and is composed of the following fields:
    1. Key [required] the name of the lock. it must match the same value used when the lock was acquired
    2. Owner [required] a unique identifier of the owner. it must match the same value used when the lock was acquired
    3. Value [not used]
    4. TypeCode [not used]
    5. Type [deprecated; not used]

Returns a ReleaseResponse

The following errors can be returned:

  1. ErrResourceNotFound will be returned if a lock with the given key wasn't found
  2. ErrLockCollision if the lock is acquired by a different owner

ReleaseResponse

The release response is currently empty. The client will have to use the returned error to determine if the lock was successfully released.

FetchAllRequest

Fetch all acquired locks by lock type. The lock type is mandatory. A FetchAllRequest should be passed a type field. It can be either a TypeCode of value LOCK (1) or PRESENCE (2), or a Type string of value lock or presence. Other values of Type or TypeCode are invalid and will return an error. Type is deprecated and will be removed in the next major version of Diego.

  1. Type: [deprecated; optional] only locks with this type will be returned in the response
  2. TypeCode: [optional] only locks with this type will be returned in the response

Returns FetchAllResponse

Only grpc or sql errors can be returned for this request

FetchAllResponse

A FetchAllResponse will include the following field:

  1. Resources: an array of Resource objects corresponding to locks that match the Type or TypeCode specified in the FetchAllRequest.

FetchRequest

Fetch a single lock by key. A FetchRequest is composed of the following field:

  1. Key [required] the unique identifier of the lock

Returns FetchResponse

The following errors can be returned:

  1. ErrResourceNotFound will be returned if a lock with the given key wasn't found

FetchResponse

A FetchResponse will include the following field:

  1. Resource the resource that was requested. A grpc error will be returned if the resource with the given key was not found.

SQL

For a description of Locket database schema see how-locket-is-using-database.md