### What problem does this PR solve?
A and B, two API servers and a REDIS server.
If A and REDIS restart, B will hold the obsolete secret key and will
lead to error.
TODO:
app.config['SECRET_KEY'] and app.secret_key still hold obsolete secret
key.
### Type of change
- [x] Bug Fix (non-breaking change which fixes an issue)
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Signed-off-by: Jin Hai <haijin.chn@gmail.com>