Create#

Introduction#

Tip

Executors use docarray.BaseDoc and docarray.DocList` as their input and output data structure. Read DocArray’s docs to see how it works.

An Executor is a self-contained microservice exposed using a gRPC or HTTP protocol. It contains functions (decorated with @requests) that process Documents. Executors follow these principles:

An Executor should subclass directly from the jina.Executor class.
An Executor is a Python class; it can contain any number of functions.
Functions decorated by requests are exposed as services according to their on= endpoint. These functions can be coroutines (async def) or regular functions. They can work on single Documents, or on batches. This will be explained later in Add Endpoints Section
(Beta) Functions decorated by write above their requests decoration, are considered to update the internal state of the Executor. The __init__ and close methods are exceptions. The reasons this is useful is explained in Stateful-executor.

Create an Executor#

To create your Executor, run:

jina hub new

You can ignore the advanced configuration and just provide the Executor name and path. For instance, choose MyExecutor.

After running the command, a project with the following structure will be generated:

MyExecutor/
├── executor.py
├── config.yml
├── README.md
└── requirements.txt

executor.py contains your Executor’s main logic. The command should generate the following boilerplate code:

from jina import Executor, requests
from docarray import DocList, BaseDoc

class MyExecutor(Executor):
    @requests
    def foo(self, docs: DocList[BaseDoc], **kwargs) -> DocList[BaseDoc]:
        pass

config.yml is the Executor’s configuration file, where you can define __init__ arguments using the with keyword.
requirements.txt describes the Executor’s Python dependencies.
README.md describes how to use your Executor.

For a more detailed breakdown of the file structure, see here.

Constructor#

You only need to implement __init__ if your Executor contains initial state.

If your Executor has __init__, it needs to carry **kwargs in the signature and call super().__init__(**kwargs) in the body:

from jina import Executor


class MyExecutor(Executor):
    def __init__(self, foo: str, bar: int, **kwargs):
        super().__init__(**kwargs)
        self.bar = bar
        self.foo = foo

What is inside kwargs?

Here, kwargs are reserved for Jina to inject metas and requests (representing the request-to-function mapping) values when the Executor is used inside a Flow.

You can access the values of these arguments in the __init__ body via self.metas/self.requests/self.runtime_args, or modify their values before passing them to super().__init__().

Since Executors are runnable through YAML configurations, user-defined constructor arguments can be overridden using the Executor YAML with keyword.

Destructor#

You might need to execute some logic when your Executor’s destructor is called.

For example, if you want to persist data to disk (e.g. in-memory indexed data, fine-tuned model,…) you can overwrite the close() method and add your logic.

Jina ensures the close() method is executed when the Executor is terminated inside a Deployment or Flow, or when deployed in any cloud-native environment.

You can think of this as Jina using the Executor as a context manager, making sure that the close() method is always executed.

from jina import Executor


class MyExec(Executor):
    def close(self):
        print('closing...')

Attributes#

When implementing an Executor, if your Executor overrides __init__, it needs to carry **kwargs in the signature and call super().__init__(**kwargs)

from jina import Executor


class MyExecutor(Executor):
    def __init__(self, foo: str, bar: int, **kwargs):
        super().__init__(**kwargs)
        self.bar = bar
        self.foo = foo

This is important because when an Executor is instantiated (whether with Deployment or flow), Jina adds extra arguments.

Some of these arguments can be used when developing the internal logic of the Executor.

These special arguments are workspace, requests, metas, runtime_args.

`workspace`#

Each Executor has a special workspace that is reserved for that specific Executor instance. The .workspace property contains the path to this workspace.

This workspace is based on the workspace passed when orchestrating the Executor: Deployment(..., workspace='path/to/workspace/')/flow.add(..., workspace='path/to/workspace/'). The final workspace is generated by appending '/<executor_name>/<shard_id>/'.

This can be provided to the Executor via the Python API or YAML API.

Hint: Default workspace

If you haven’t provided a workspace, the Executor uses a default workspace, defined in ~/.cache/jina/.

`requests`#

By default, an Executor object contains requests as an attribute when loaded. This attribute is a Dict describing the mapping between Executor methods and network endpoints: It holds endpoint strings as keys, and pointers to functions as values.

These can be provided to the Executor via the Python API or YAML API.

`metas`#

An Executor object contains metas as an attribute when loaded from the Flow. It is of SimpleNamespace type and contains some key-value information.

The list of the metas are:

name: Name given to the Executor;
description: Description of the Executor (optional, reserved for future-use in auto-docs);

These can be provided to the Executor via Python or YAML API.

`runtime_args`#

By default, an Executor object contains runtime_args as an attribute when loaded. It is of SimpleNamespace type and contains information in key-value format. As the name suggests, runtime_args are dynamically determined during runtime, meaning that you don’t know the value before running the Executor. These values are often related to the system/network environment around the Executor, and less about the Executor itself, like shard_id and replicas.

The list of the runtime_args is:

name: Name given to the Executor. This is dynamically adapted from the name in metas and depends on some additional arguments like shard_id.
replicas: Number of replicas of the same Executor deployed.
shards: Number of shards of the same Executor deployed.
shard_id: Identifier of the shard corresponding to the given Executor instance.
workspace: Path to be used by the Executor. Note that the actual workspace directory used by the Executor is obtained by appending '/<executor_name>/<shard_id>/' to this value.
py_modules: Python package path e.g. foo.bar.package.module or file path to the modules needed to import the Executor.

You cannot provide these through any API. They are generated by the orchestration mechanism, be it a Deployment or a Flow.

Tips#

Use jina hub new CLI to create an Executor: To create an Executor, always use this command and follow the instructions. This ensures the correct file structure.
You don’t need to manually write a Dockerfile: The build system automatically generates an optimized Dockerfile according to your Executor package.

Tip

In the jina hub new wizard you can choose from four Dockerfile templates: cpu, tf-gpu, torch-gpu, and jax-gpu.

Stateful-Executor (Beta)#

Executors may sometimes contain an internal state which changes when some of their methods are called. For instance, an Executor could contain an index of Documents to perform vector search.

In these cases, orchestrating these Executors can be tougher than it would be for Executors that never change their inner state (Imagine a Machine Learning model served via an Executor that never updates its weights during its lifetime). The challenge is guaranteeing consistency between replicas of the same Executor inside the same Deployment.

To provide this consistency, Executors can mark some of their exposed methods as write. This indicates that calls to these endpoints must be consistently replicated between all the replicas such that other endpoints can serve independently of the replica that is hit.

Deterministic state update

Another factor to consider is that the Executor’s inner state must evolve in a deterministic manner if we want replicas to behave consistently.

By considering this, Executors can be scaled in a consistent manner.

Snapshots and restoring#

In a Stateful Executor Jina uses the RAFT consensus algorithm to guarantee that every replica eventually holds the same inner state. RAFT writes the incoming requests as logs to local storage in every replica to ensure this is achieved.

This could become problematic if the Executor runs for a long time as log files could grow indefinitely. However, you can avoid this problem by describing the methods def snapshot(self, snapshot_dir) and def restore(self, snapshot_dir) that are triggered via the RAFT protocol, allowing the Executor to store its current state or to recover its state from a snapshot. With this mechanism, RAFT can keep cleaning old logs by assuming that the state of the Executor at a given time is determined by its latest snapshot and the application of all requests that arrived since the last snapshot. The RAFT algorithm keeps track of all these details.

Create#

Introduction#

Create an Executor#

Constructor#

Destructor#

Attributes#

workspace#

requests#

metas#

runtime_args#

Tips#

Stateful-Executor (Beta)#

Snapshots and restoring#

`workspace`#

`requests`#

`metas`#

`runtime_args`#