Custom modules

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💡 You are looking at older or release candidate documentation. The current Weaviate version is v1.15.2


Besides using one of the out-of-the-box vectorization models, you can also attach your own machine learning model to Weaviate. This way, you can use Weaviate to scale your ML and NLP models, since Weaviate takes care of efficient data storage and retrieval. A custom vectorizer module is for example a model that you trained on your own training data, that is able to transform data (e.g. text or image data) to embeddings.

If you have model that already fits with an existing model architecture (e.g. Transformers), you don’t have to write any custom code and you can just run this Transformer model with the existing text2vec-transformer module.

This page contains information about how you can attach your own ML model to Weaviate. You will need to attach your ML model to Weaviate’s Module API as a module. First, there is some information about how (vectorizer/embedding) modules in Weaviate work.

Background: Module architecture in Weaviate

To understand how to create a new module, you’ll need to understand how the module system of Weaviate works in general.

Weaviate is entirely agnostic of how a module obtains the values it needs for the specific lifecycle hooks. For example, for a vectorizer module, the contract between Weaviate and the module is the following: At import time, each object is passed to the (configured) vectorizer module and the module must extend it with a vector (embedding). Weaviate is agnostic to how the module does that. For example if the module’s purpose is to use a pre-existing ML model for inference, the module may decide to provide a second inference service and contact that inference service as part of the “vectorize” lifecycle hook. Weaviate is agnostic of how that communication occurs. For example the text2vec-contextionary module uses a gRPC API on its inference service, whereas the the text2vec-transformers module uses a REST API for the same purpose.

Typically a (vectorizer) module consists of two parts:

  1. Module code for Weaviate, written in Go, which hooks into specific lifecycles and provides various capabilities (like controlling the API function) to integrate the module into the regular flow in Weaviate.
  2. Inference service, typically a containerized application that wraps an ML model with a module-specific API which is consumed by the module code executed in Weaviate (part 1).

The visualization below shows how modules are part of and connected to Weaviate. The black border indicates Weaviate Core, with the grey boxes as internals. Everything in red involves how Weaviate uses the modules that are connected, with the general Module System API. The red Module API spans two internal ‘layers’, because it can influence the Weaviate APIs (e.g. by extending GraphQL or providing additional properties), and it can influence the business logic (e.g. by taking the properties of an object and setting a vector).

Everything that is blue belongs to a specific module (more than one module can be attached, but here we show one module). Here we have the example of Weaviate using the text2vec-transformers module bert-base-uncased. Everything that belongs to the text2vec-transformers module is thus drawn in blue. The blue box inside Weaviate Core is the part 1 of the module: the module code for Weaviate. The blue box outside Weaviate Core is the separate inference service, part 2.

The picture shows three APIs:

  • The first grey box inside Weaviate Core, which is the user-facing RESTful and GraphQL API.
  • The red box is the Module System API, which are interfaces written in Go.
  • The third API is completely owned by the module, which is used to communicate with the separate module container. This is in this case a Python container, shown on the left.

To use a custom ML model with Weaviate, you have two options: (further explained below)

  • A: Replace parts of an existing module, where you only replace the inference service (part 2). You don’t have to touch Weaviate Core here.
  • B: Build a complete new module and replace all existing (blue) module parts (both 1 and 2). You can configure custom behavior like extending the GraphQL API, as long as the module can hook into the ‘red’ Module System API. Keep in mind that you’ll need to write some module code in Go to achieve this.

Weaviate module APIs overview

Let’s take a more detailed example of how you configure Weaviate to use a specific module: if we look at the text2vec-transformers module, you set ENABLE_MODULES=text2vec-transformers in the docker-compose configuration, which instructs Weaviate to load the respective Go code (part 1). Additionally, you include another service in docker-compose.yml which contains the actual model for inference (part 2). In more detail, let’s look at how a specific (GraphQL) function is implemented in the text2vec-transformers module:

  1. Module code for Weaviate, written in Go:
    • Tells the Weaviate GraphQL API that the module provides a specific nearText method.
    • Validates specific configuration and schema settings and makes them available to the APIs.
    • Tells Weaviate how to obtain a vector (e.g. a word or image embedding) when one is necessary (by sending an HTTP request to a third-party service, in this case the Python application around the inference model)
  2. Inference service:
    • Provides a service that can do model inference.
    • Implements an API that is in contract with A (not with Weaviate itself).

Note that this is just one example, and variations are possible as long as both part 1 and 2 are present where 1 contains the connection to Weaviate in Go and 2 contains that inference model that part 1 uses. It would also be possible to amend for example the Weaviate text2vec-transformers module (part 1) to use the Huggingface API or some other third-party hosted inference service, instead of it’s own container (now in part 2) that it brings.

A module completely controls the communication with any container or service it depends on. So for example in the text2vec-transformers module, the API of the inference container is a REST API. But for the text2vec-contextionary module has a gRPC, rather than a REST API or another protocol.

Module characteristics

A module is a custom code that can extend Weaviate by hooking into specific lifecycle hooks. As Weaviate is written in Go, so module code must also be written in Go. However, some existing modules make use of independent services which can be written in any language, as is often the case with vectorizer modules which bring along model inference containers often written in Python.

Modules can be “vectorizers” (defines how the numbers in the vectors are chosen from the data) or other modules providing additional functions like question answering, custom classification, etc. Modules have the following characteristics:

  • Naming convention:
    • Vectorizer: <media>2vec-<name>-<optional>, for example text2vec-contextionary, image2vec-RESNET or text2vec-transformers.
    • Other modules: <functionality>-<name>-<optional>.
    • A module name must be url-safe, meaning it must not contain any characters which would require url-encoding.
    • A module name is not case-sensitive. text2vec-bert would be the same module as text2vec-BERT.
  • Module information is accessible through the v1/modules/<module-name>/<module-specific-endpoint> RESTful endpoint.
  • General module information (which modules are attached, version, etc.) is accessible through Weaviate’s v1/meta endpoint.
  • Modules can add additional properties in the RESTful API and _additional properties in the GraphQL API.
  • A module can add filters in GraphQL queries.
  • Which vectorizer and other modules are applied to which data classes is configured in the schema.

How to build and use a custom module

There are two different ways to extend Weaviate with custom vectorization capabilities: You can either build a completely custom module (parts 1 + 2) or only replace the inference service of an existing module (only replace part 2, Option A). The latter is a good option for fast prototyping and proofs of concepts. In this case, you simply replace the inference model (part 2), but keep the interface with Weaviate in Go. This is a quick way to integrate completely different model types. You can also choose to build a complete new module (Option B). This is the most flexible option, but it means you’ll have to write a Weaviate interface in Go. We recommend to only go for option B if you are happy with the prototype results. With option B you can turn the PoC into a full module, because you can control all configuration and naming when you go for option B.

A. Replace parts of an existing module

The quickest way to integrate a completely different inference model is replacing parts of an existing module. You reuse part 1 (the interface with Weaviate) and thus adhere to part 1’s API contract, and only implement changes to or replace part 2.

Because you are not touching the Go Weaviate interface code, you don’t have the possibility to introduce new configuration that is specific to your module inference into Weaviate’s APIs provided and consumed by existing modules that are not existing in part 1 (i.e. all the configuration parameters, e.g. those of text2vec-transformers). This also implies that you cannot change or introduce new (GraphQL) API functions or filters. Note that Weaviate APIs are not guaranteed to be stable. Even on a non-breaking Weaviate release, ‘internal’ APIS could always change.

To use a new inference model (part 2) with an existing Weaviate interface (part 1), you could reuse all the Go-code from the existing module and simply point it to a different inference container. As an example, here’s how to use a custom inference module using the text2vec-transformers Go-code:

  1. In a valid docker-compose.yml that’s configured to use transformers, you will find an env var like this: TRANSFORMERS_INFERENCE_API: 'http://t2v-transformers:8080', you can point that to any app you like. You should keep the variable name TRANSFORMERS_INFERENCE_API.
  2. Build a small HTTP API wrapper around your model, it should at the minimum have the endpoints listed below (which is in this example entirely specific to the text2vec-transformers module and fully in its control):
    1. GET /.well-known/live -> respond 204 when the app is alive
    2. GET /.well-known/ready -> respond 204 when the app is ready to serve traffic
    3. GET /meta -> respond meta information about the inference model
    4. POST /vectors -> see example request and response payloads below. (Note that the app is exposed locally on port 8090 on my machine by adding ports: ["8090:8080"] in the docker-compose file).


curl localhost:8090/vectors/ -H "Content-Type: application/json" -d '{"text":"hello world"}' 


{"text":"hello world","vector":[-0.08469954133033752,0.4564870595932007, ..., 0.14153483510017395],"dim":384} 

B. Build a completely new module

Implementing a full new module with both part 1 and 2 is a lot more free, because you can control naming, APIs, behavior, etc. To achieve this, you are essentially contributing to Weaviate. Note that for this option, you need to understand at least parts of Weaviate’s architecture, and what a module can control and what not (what is “fixed”). You can fork Weaviate’s repository and create a completely new module inside it. This new module can also depend on any number of other containers (which you will have to supply), and could use any API for communication with its dependencies (it could also have not any dependencies).

The Go API interfaces are documented in the code as comments (example). All interfaces that make up a module can be found in this package. A (new) module does not need to implement all these interfaces. For each interface, you can make the decision whether you want to provide that capability in your module or not. For each capability Weaviate only considers the modules that do implement it.

A good starting point would be to look at the text2vec-transformers module (which is much simpler than the text2vec-contextionary). If you want to create a module really similar to this module, but you, for example, don’t want the module to provide any GraphQL _additional properties, you can skip this interface entirely.

If you choose to build a completely new module including a Weaviate Go interface, you can contact us via Slack or through an issue on Github so we help you getting started.

Important notes

  • The length of the vectors your vectorizer has influences later usage, for example if you’re exploring your data by vector with the GraphQL explore filter, the length of this vector should match with the vector length of the data points.
  • Weaviate APIs internal to a module are not guaranteed to be stable. Even on a non-breaking Weaviate release, ‘internal’ APIS could always change.

More resources

If you can’t find the answer to your question here, please look at the:

  1. Frequently Asked Questions. Or,
  2. Knowledge base of old issues. Or,
  3. For questions: Stackoverflow. Or,
  4. For issues: Github. Or,
  5. Ask your question in the Slack channel: Slack.