[Bug] Ray master fails to start dashboard as a result of new aiohttp version (3.8)

[gilfree]

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• I searched the issues and found no similar issues.

Ray Component

Ray Core

What happened + What you expected to happen

After installing nightly, ray start fails to start dashboard because of missing import aiohttp.signals.

I ran

RAY_OBJECT_STORE_ALLOW_LOW_STORAGE=1 ray start --head --include-dashboard 1 --port 0

And got:
ImportError: Not all Ray Dashboard dependencies were found. To use the dashboard please install Ray using pip install ray[default].

When manually trying to do:
python -c 'import ray.dashboard.optional_deps'
I get ModuleNotFoundError: No module named 'aiohttp.signals'

Which is expected as recently aiohttp released version 3.8 which lacks the above import:
see: aio-libs/aiohttp#5293

Versions / Dependencies

nightly ray on ubuntu 18.04 python 3.7

Reproduction script

#! /bin/bash
set -x
python3 -mvenv venv
venv/bin/python -m pip install -U pip
venv/bin/python -m pip install --trusted-host s3-us-west-2.amazonaws.com -U 'ray[default] @ https://s3-us-west-2.amazonaws.com/ray-wheels/latest/ray-2.0.0.dev0-cp37-cp37m-manylinux2014_x86_64.whl'
venv/bin/python -c 'import ray.dashboard.optional_deps'
RAY_OBJECT_STORE_ALLOW_LOW_STORAGE=1 ray start --head --include-dashboard 1 --port 0

Anything else

No response

Are you willing to submit a PR?

• Yes I am willing to submit a PR!

[ebr]

We are also affected by this; confirmed that pip install 'aiohttp<3.8' on all nodes fixes the issue.

[jamesmishra]

I believe that this issue was fixed when PR #20261 was landed into master.