Improve dependency management

[ZanSara]

The current handling of dependencies is quite monolithic: users must install them all regardless of the subset of features they want to use. We should make Haystack more modular at install time.

Options

Nowadays there are several ways to properly handle dependency groups:

• several requirement.txt files: quite old fashioned by now and a bit harder to manage
• extras_require in setup.py: "traditional" way, safe and widely used
• pyproject.toml: the new way, as recommended by PEP517 and PEP660.

Proposed dependency groups

• minimal: basic Haystack on CPU with one single document store (inMemory maybe)
• gpu: for running Haystack on GPU
• rest: install also the REST server API deps
• ui: install Streamlit deps
• demo: rest + ui
• ci: for GitHub runners
• win: for Windows installs (if possible)
• colab: to workaround Colab specific issues when necessary
• One group for each document store
• all_doc_stores: install all possible dependency from document stores
• test for the test dependencies
• docs: for building documentation
• code: black, linter and possible extra tools if/when we introduce them
• all (or dev): complete dependency list for development and contributing. Includes all of the above.

We can also consider adding smaller groups for special components with exotic dependencies, like crawler, ocr, etc.

Default install

It's up to debate what the default install (pip install haystack) should look like.

The important point is that the dependencies that are installed in this case must be marked as mandatory. This at least is the case for extras_require in setup.py, and might have changed in pyproject.toml. If it's the case, the default install should be effectively a minimal install. For example, if we include GPU deps in this group, they will become mandatory, and having a pure CPU install will be impossible.

I will investigate the options and update this section with new information.

Related issues

Related to #1291, #1716, #1826, #1806

Closes #1070

Next steps

• Learn more about what's currently possible with pyproject.toml and whether all of our dependencies can actually work with it. As of last year that were still some issues with large libraries that needed complex build steps.
• Finalize dependency groups list
• Define what a default install should look like
• Investigate how to properly handle failed imports for unmet dependencies
• Fix dependency related issues (like Improve Colab setup experience by simplifying dependencies #1806)

[ZanSara]

@tholor @oryx1729 @julian-risch @tstadel @askainet @brandenchan @bogdankostic @lalitpagaria: Let me know what do you think about the dependency groups and if you have any opinions about the topic 🙂

[lalitpagaria]

I feel many groups may confuse the users. Small options might be good like core, minimal, all , colab etc. So if anyone likes their customization for example mentioned in #1716 they can use minimal and then install whatever they like.

Not related to this task but how about a CLI utility that takes pipeline YAML as input and lists or installs required dependencies to run that pipeline smoothly.

[tholor]

I agree with @lalitpagaria and would reduce the groups a bit:

minimal: basic Haystack on CPU with one single document store (inMemory maybe)
gpu: for running Haystack on GPU
rest: install also the REST server API deps
ui: install Streamlit deps
demo: rest + ui
ci: for GitHub runners => Not sure, but we can probably use dev or all in the CI
win: for Windows installs (if possible)
colab: to workaround Colab specific issues when necessary
One group for each document store
all_doc_stores: install all possible dependency from document stores
test for the test dependencies
docs: for building documentation
code: black, linter and possible extra tools if/when we introduce them
=> group the above three as dev
all (or dev): complete dependency list for development and contributing. Includes all of the above.

Not sure how many dependencies we have for "preprocessing / conversion", but might also be an extra category "preprocessing".

Thinking about which version is the "default", we might also consider something between "minimal" and "all". Maybe really just calling it internally default or standard.

Also: I think once we have the basic structure implemented it will be rather easy to extend the list of options here if we see the need.

[ZanSara]

Thank you both for the feedback! I'm ok reducing the groups of course. I like @tholor's list except for the demo related deps: I think many people would like to use the REST API with their own frontend, so I'd rather keep rest and ui and remove demo.
Regarding preprocessing, I agree many weird deps will go here so probably it makes sense. On the other hand, if it ends up being fundamental for most users, making a separate group could be confusing.

Proposed list:

• minimal: basic Haystack on CPU with one single document store (inMemory maybe)
• gpu: for running Haystack on GPU
• rest: install also the REST server API deps
• ui: install Streamlit deps
• win: for Windows installs (if possible)
• colab: to workaround Colab specific issues when necessary
• elasticsearch, faiss, milvus, milvus2, weaviate, graphdb, all_doc_stores
• dev: test, docs and dev tools
• all: complete dependency list for development and contributing. Includes all of the above.
• preprocessing: to verify

That makes for 15(16) categories. Many indeed, but most users will not need to know about them anyway.

Note also that this syntax pip install haystack[rest,ui] is totally valid, so having a bit more groups helps granularity without making the installation too complex