models - ollama - init async client per request

[pgrayy]

Description

The Ollama AsyncClient has an issue where making multiple requests with separate asyncio.run() calls causes the second request to fail with "Event loop is closed" error. The reason is that AsyncClient uses httpx internally, which maintains a connection pool that persists beyond individual event loops. This means connections created in the first event loop remain in the pool after that loop closes, and when the second asyncio.run() creates a new event loop, httpx tries to reuse those existing pooled connections that are still tied to the first event loop instead of the new event loop, thus causing a failure.

This is a problem for Strands as Agent.__call__ runs asyncio.run() on every invocation. Consequently, doing something like the following with the OllamaModel provider will fail:

from strands import Agent
from strands.models.ollama import OllamaModel

model = OllamaModel(host="http://localhost:11434", model_id="mistral-nemo")
agent = Agent(model=model)

agent("Hello")
agent("Hello again")  # Event loop is closed encountered

The fix is to establish a new Ollama AsyncClient connection on every call to stream. This fits with the pattern documented in both the Ollama docs and the httpx docs.

Related Issues

#431

Documentation PR

N/A

Type of Change

• Bug fix
• New feature
• Breaking change
• Documentation update
• Other (please describe):

Testing

How have you tested the change? Verify that the changes do not break functionality or introduce warnings in consuming repositories: agents-docs, agents-tools, agents-cli

• I ran hatch run prepare
• Ran hatch test tests_integ/models/test_model_ollama.py
• Ran the following test script:

import gc
from strands import Agent
from strands.models.ollama import OllamaModel

model = OllamaModel(host="http://localhost:11434", model_id="tinyllama")

for _ in range(10):
    agent = Agent(model=model)
    agent("what is 2+2")

    gc.collect()

Checklist

• I have read the CONTRIBUTING document
• I have added any necessary tests that prove my fix is effective or my feature works
• I have updated the documentation accordingly
• I have added an appropriate example to the documentation to outline the feature, or no new docs are needed
• My changes generate no new warnings
• Any dependent changes have been merged and published

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