Pipelines

Pipelines are powerful and highly flexible systems that form the engine for your app. They consist of components that process your data and perform various tasks on it. Each component in a pipeline passes its output to the next component.

---

How Do Pipelines Work?

Pipelines are composed of connected components. Each component processes a piece of your data, such as documents, and performs specific tasks before passing the output to the next component. For example, a basic RAG pipeline may include:

• A TextEmbedder that takes the user query and turns it into a vector.
• A Retriever that receives the vector from the TextEmbedder and uses it to fetch relevant documents from the document store.
• A PromptBuilder that injects the user query and the documents from the Retriever into the prompt.
• A Generator that uses the prompt from the PromptBuilder, including the documents, to generate the response.

Components function like modular building blocks that you can mix, match, and replace to form various pipeline configurations, such as loops, branches, or simultaneous flows. When connecting the components, it's crucial to ensure the output type of one component matches the input type of the next. Each component receives only the data it needs, which speeds up the pipeline and makes it easier to debug.

For component compatibility, check individual pages under Pipeline Components.

Haystack Enterprise Platform uses Haystack pipelines, which means pipelines accept Haystack objects as input and output. For more information, see Haystack documentation.

Connection Types

Pipelines in Haystack Enterprise Platform are flexible and multifunctional. While you can still create simple pipelines performing one function, like answering queries, you can also use them to build complex workflows.

Smart Connections

Components connect when their input and output types are compatible. In most cases, the types must match. However, Haystack Platform pipelines also support smart connections for certain type combinations:

• List types: You can connect multiple lists of the same type to a component that accepts a list as input. For example, you can connect multiple Converters that produce lists of documents to a DocumentWriter that accepts a list of documents as input. The pipeline combines the lists into a single list and passes it to the component.

• String to ChatMessage: A string automatically converts to a ChatMessage with the user role. This is useful when you pass plain text to a ChatPromptBuilder or ChatGenerator.

• ChatMessage to string or a list of strings or a list of ChatMessage: This conversion makes it possible to connect a ChatGenerator to inputs such as the query parameter of a Retriever.

• List of string to a string or ChatMessage: Pipelines support connections between list of strings and components that accept a single string or ChatMessage. For example, an OpenAIGenerator's replies can connect to OpenSearchHybridRetriever's query.

• List of ChatMessage to a single ChatMessage or string: The pipeline supports connections between lists of ChatMessages and components that accept a single ChatMessage or string. For example, OpenAIChatGenerator's messages can connect to OpenSearchHybridRetriever's query.

This table summarizes connections between input and output types enabled by smart connections:

Sender Output Type	Receiver Input Type	What happens
List of Documents (multiple senders to same input)	List of Documents	Lists are merged into one.
List of ChatMessage (multiple senders to same input)	List of ChatMessage	Lists are merged into one.
List of strings (multiple senders to same input)	List of strings	Lists are merged into one.
string	ChatMessage	Converted to a ChatMessage with the user role.
ChatMessage	string	Content is extracted as a string.
List of ChatMessage	string or ChatMessage	First message is used (for example, as a query).
List of string	string or ChatMessage	First string is used.

This table shows component-level connections for both list merging and type conversions:

Sender	Receiver	What Happens
BM25 Retriever, Embedding Retriever output: documents	Rankers (for example, TransformersSimilarityRanker) input: documents	List merge
Ranker or multiple retrievers output: documents	PromptBuilder, AnswerBuilder input: documents (if configured in the template)	List merge
Ranker or multiple retrievers output: documents	ChatPromptBuilder input: documents	List merge
Multiple converters output: documents	DocumentSplitter input: documents	List merge
Multiple converters or DocumentSplitter output: documents	DocumentWriter input: documents	List merge
Multiple converters or DocumentSplitter output: documents	Document Embedders (for example SentenceTransformersDocumentEmbedder) input: documents	List merge
ChatPromptBuilder output: prompt DeepsetChatHistoryParser output: messages	Agent input: messages	List merge
Generator, ChatGenerator output: replies	Retriever, Ranker, AnswerBuilder input: query PromptBuilder input: question	List of ChatMessages converted to string
ChatGenerator output: replies	AnswerBuilder input: replies	Type conversion
Agent output: last_message	SentenceTransformersTextEmbedder input: text Retriever input: query	Type conversion

Smart connections make many "glue" components like DocumentJoiner, ListJoiner, and OutputAdapter unnecessary. To learn how to update your existing pipelines, see Simplify Your Pipelines with Smart Connections.

Connection Validation

When you connect components in a pipeline, it validates that their outputs and inputs match and are explicitly indicated and, if needed, produces detailed errors.

Branches

Pipelines can branch to process data simultaneously. For example, each pipeline branch can have a different converter, each dedicated to a specific file type, allowing for efficient parallel processing.

Loops

In loops, components operate iteratively, with a set limit on repetitions. This is useful in scenarios such as self-correcting loops, where a validator component checks the generator's output and potentially cycles it back for correction until it meets the quality standard and can be sent further down the pipeline.

How Do Pipelines Use Your Files?

Pipelines run on the documents produced by the indexes they're connected to. An index preprocesses the files from a Haystack Platform workspace, converts them into documents, and writes them into a document store where a pipeline can access them. A single pipeline can be connected to multiple indexes. For details, see Indexes.

One file may produce multiple documents. Documents inherit metadata from files. Your indexing pipeline defines the exact steps for preprocessing the files.

Building Pipelines

Pipelines contain recipes for how to execute a query. A typical pipeline that runs on your files in Haystack Platform, receives the user query, retrieves the relevant documents, and processes them through the components to arrive at an answer.

Example of a pipeline

components:
  bm25_retriever:
    # Selects the most similar documents from the document store
    type: haystack_integrations.components.retrievers.opensearch.bm25_retriever.OpenSearchBM25Retriever
    init_parameters:
      document_store:
        init_parameters:
          use_ssl: True
          verify_certs: False
          hosts:
          - ${OPENSEARCH_HOST}
          http_auth:
          - "${OPENSEARCH_USER}"
          - "${OPENSEARCH_PASSWORD}"
          index: Standard-Index-English
          max_chunk_bytes: 104857600
          embedding_dim: 768
          return_embedding: false
          method:
          mappings:
          settings:
          create_index: true
          timeout:
        type: haystack_integrations.document_stores.opensearch.document_store.OpenSearchDocumentStore
      top_k: 20 # The number of results to return

    query_embedder:
      type: haystack.components.embedders.sentence_transformers_text_embedder.SentenceTransformersTextEmbedder
      init_parameters:
        model: "intfloat/e5-base-v2"
        device: null

  embedding_retriever:
    # Selects the most similar documents from the document store
    type: haystack_integrations.components.retrievers.opensearch.embedding_retriever.OpenSearchEmbeddingRetriever
    init_parameters:
      document_store:
        init_parameters:
          use_ssl: True
          verify_certs: False
          http_auth:
          - "${OPENSEARCH_USER}"
          - "${OPENSEARCH_PASSWORD}"
          hosts:
          index: ""
          max_chunk_bytes: 104857600
          embedding_dim: 768
          return_embedding: false
          method:
          mappings:
          settings:
          create_index: true
          timeout:
        type: haystack_integrations.document_stores.opensearch.document_store.OpenSearchDocumentStore
      top_k: 20 # The number of results to return

    document_joiner:
      type: haystack.components.joiners.document_joiner.DocumentJoiner
      init_parameters:
        join_mode: concatenate

    ranker:
      type: haystack.components.rankers.transformers_similarity.TransformersSimilarityRanker
      init_parameters:
        model: "intfloat/simlm-msmarco-reranker"
        top_k: 8
        device: null
        model_kwargs:
          torch_dtype: "torch.float16"

    prompt_builder:
      type: haystack.components.builders.prompt_builder.PromptBuilder
      init_parameters:
        template: |-
          You are a technical expert.
          You answer questions truthfully based on provided documents.
          Ignore typing errors in the question.
          For each document check whether it is related to the question.
          Only use documents that are related to the question to answer it.
          Ignore documents that are not related to the question.
          If the answer exists in several documents, summarize them.
          Only answer based on the documents provided. Don't make things up.
          Don't reference documents.
          Just output the structured, informative and precise answer and nothing else.
          If the documents can't answer the question, say so.
          These are the documents:
          {% for document in documents %}
          Document[{{ loop.index }}]:
          {{ document.content }}
          {% endfor %}
          Question: {{question}}
          Answer:

  llm:
    type: haystack.components.generators.openai.OpenAIGenerator
    init_parameters:
      api_key:
        "type": "env_var"
        "env_vars":
        - "OPENAI_API_KEY"
        "strict": False
      model: "gpt-4o"
      generation_kwargs:
        max_tokens: 400
        temperature: 0.0
        seed: 0

    answer_builder:
      init_parameters: {}
      type: haystack.components.builders.answer_builder.AnswerBuilder

connections:  # Defines how the components are connected
  - sender: bm25_retriever.documents
    receiver: document_joiner.documents
  - sender: query_embedder.embedding
    receiver: embedding_retriever.query_embedding
  - sender: embedding_retriever.documents
    receiver: document_joiner.documents
  - sender: document_joiner.documents
    receiver: ranker.documents
  - sender: ranker.documents
    receiver: prompt_builder.documents
  - sender: ranker.documents
    receiver: answer_builder.documents
  - sender: prompt_builder.prompt
    receiver: llm.prompt
  - sender: llm.replies
    receiver: answer_builder.replies

max_loops_allowed: 100

inputs:  # Define the inputs for your pipeline
   query:  # These components will receive the query as input
    - "bm25_retriever.query"
    - "query_embedder.text"
    - "ranker.query"
    - "prompt_builder.question"
    - "answer_builder.query"

   filters:  # These components will receive a potential query filter as input
    - "bm25_retriever.filters"
    - "embedding_retriever.filters"

outputs:  # Defines the output of your pipeline
    documents: "ranker.documents"  # The output of the pipeline is the retrieved documents
    answers: "answer_builder.answers"  # The output of the pipeline is the generated answer

Inputs

Pipelines always take Input as the first component. When working in Builder, drag Input from the Inputs group onto the canvas and then connect it to the components that should receive its outputs.

When working in YAML editor, you must explicitly specify the inputs and the components that receive them:

inputs:  # Define the inputs for your pipeline
  query:  # These components will receive the query as input
  - "bm25_retriever.query"
  - "query_embedder.text"
  - "ranker.query"
  - "prompt_builder.question"
  - "answer_builder.query"

  filters:  # These components will receive a potential query filter as input
  - "bm25_retriever.filters"
  - "embedding_retriever.filters"

Filters are documents' metadata keys by default. This means that if your documents have the following metadata: {"category": "news"}, when searching in Playground, users can narrow down the search to the documents matching this category. You can also pass filters at search time with the Search endpoint. For more information about filters, see Working with Metadata.

Outputs

The output of pipelines matches the output of the last component. However, it must be one of the following data classes:

• List of Document objects (usually document search pipelines)
• List of Answer objects, including the following subclasses:
  • List of ExtractedAnswer objects (usually extractive question answering pipelines)
  • List of GeneratedAnswer objects (usually RAG pipelines or pipelines that use large language models to generate answers)

The output can be a list of documents, a list of answers, or both. Ensure the last component in your pipeline produces one or both of these outputs. For example, you may need to add an AnswerBuilder after a Generator to produce a list of GeneratedAnswerobjects. For more information, see Pipeline Components. To learn more about data classes, see Haystack data classes.

In Builder, to finalize the pipeline with the correct output, drag the Output component onto the canvas and connect it to the components that produce the documents or answers you want to include:

When working in the YAML editor, you must explicitly specify the outputs and the components that provide them:

outputs:  # Defines the output of your pipeline
  documents: "ranker.documents"  # The output of the pipeline is the retrieved documents
  answers: "answer_builder.answers"  # The output of the pipeline is the generated answers

Pipeline Service Levels

To save costs and meet your infrastructure and service requirements, your pipelines are assigned service levels. There are three service levels available:

• Draft: This is a service level automatically assigned to new and undeployed pipelines, so that you can easily distinguish them from the deployed ones.
• Development: Pipelines at this level are designed for testing and running experiments. They have no replicas by default, and their time to standby is short, so they can save resources whenever these pipelines aren't used. When you deploy a draft pipeline, it becomes a development pipeline.
• Production: This level is recommended for business-critical scenarios where you need the pipeline to be scalable and reliable. Pipelines at this level include one replica by default and a longer time-to-standby period than other service levels. With heavy traffic, the number of replicas grows up to 10.

This table gives an overview of the default settings that come with each service level:

Service level	Description	Idle Timeout	Scaling (replicas)	How to enable
Production	Designed for critical business scenarios that require reliable and scalable pipelines.	24 hours	1 at all times, scales up to 10 if traffic is heavy	- In Haystack Enterprise Platform, on the Pipelines page - Through the Update Pipeline REST API endpoint
Development	Designed for testing and experimenting purposes.	20 minutes	0	- By switching off the Production service level for a deployed production pipeline in Haystack Enterprise Platform - Through the Update Pipeline REST API endpoint - By deploying a draft pipeline
Draft	Indicates an undeployed pipeline.	n/a	0	- By undeploying a production or development pipeline - All new pipelines are automatically classified as drafts

Idle timeout is the time after which an unused pipeline enters a standby mode to save resources. Inactive pipelines don't use up the pipeline hours included in your plan. You can customize the idle timeout for each pipeline in the pipeline's Settings tab or through the Update Pipeline REST API endpoint. The maximum idle timeout is 30 days. To use a pipeline on standby, activate it either on the Pipelines page or by initiating a search using that pipeline.

Replicas are the number of duplicate versions of a pipeline that are available. In case there is a spike in demand, Haystack Platform seamlessly switches to a functioning replica to maintain uninterrupted service. You can configure the minimum and maximum number of replicas in the pipeline's Settings tab or through the Update Pipeline REST API endpoint. The maximum number of replicas is 10.

You can change the service level of your pipeline at any time. For details, see Change the Pipeline's Service Level.

The Pipelines Page

All the pipelines created by your organization are listed on the Pipelines page. The pipelines listed under Deployed are the ones that you can run your search with. The pipelines under In Development are drafts you must deploy before you can use them for your search.

The Pipeline Details Page

Clicking a pipeline name opens Pipeline Details, where you can check all the information about your pipeline, including pipeline logs and search history. You can check the following information about the pipeline:

• ID
• Status
• Service level
• Pipeline overview
• Search history
• Logs
• Settings

Pipeline Status

Draft pipelines are not deployed. When you deploy a pipeline, it changes its status as follows:

• Deploying: The pipeline is being deployed.
• Deployed: The pipeline is ready to resolve queries.
• Failed to deploy: It's a fatal state. Your pipeline was not deployed and you can't search with it. For ideas on how to fix it, see Troubleshoot Pipeline Deployment.

Overview

The overview shows the feedback you received for your pipeline and its latency.

Search history

The Search History tab shows the queries run with this pipeline and their results. You can customize the Search History table columns to show the information you need. You can also export the entire search history as a CSV file for a specific time period. This is useful for analyzing the performance of your pipeline over time.

Logs

Use the logs to troubleshoot issues with your pipeline. You can filter the logs by message and pipeline type or date added. You can also search for keywords in log messages.

Settings

GPU Acceleration

Pipelines use CPU by default. Turn on GPU support on the Settings tab when your pipeline includes components that run better on a GPU, such as DoclingConverter, SentenceTransformersDocumentEmbedder, or custom components that use AI models.

When GPU support is on, the pipeline checks whether a component needs a GPU and assigns one automatically. GPUs are only used when required and are not reserved for the entire pipeline run.

If GPU support is off and your pipeline includes components that rely on a GPU, those components run on the CPU instead. This can slow down processing and may cause timeouts, especially for larger or more complex pipelines.

For detailed instructions, see Enable GPU Acceleration.

Pipeline Scaling

To increase availability, set the number of replicas allocated to a pipeline. Haystack Platform automatically scales replicas up or down based on traffic, and depending on the maximum and minimum number of replicas you set.

For production pipelines, set at least two replicas. This setup helps keep your pipeline available if one replica fails.

Adding more replicas can increase your costs.

Idle Timeout

Set the idle timeout to define how long a pipeline can remain inactive before it enters standby mode. When a pipeline becomes idle, Haystack Platform scales its replicas down to zero.

Idle pipelines do not consume the pipeline hours included in your plan. For example, if you set the idle timeout to 12 hours, the pipeline enters standby mode after 12 hours of inactivity.

This setting is useful for saving costs when you don't need your pipeline to be always available.