diaosj opened a new issue #3546:
URL: https://github.com/apache/apisix/issues/3546
### Issue description
Set two nodes to an upstream. Suppose they are `NodeA` and `NodeB`.
Upstream JSON is like this:
```
{"header":{"revision":"10298","cluster_id":"17817882145681418091","raft_term":"2","member_id":"12344213989818773070"},"count":"1","node":{"modifiedIndex":8878,"value":{"pass_host":"pass","nodes":{"NodeA":100,"NodeB":0},"desc":"","type":"roundrobin","create_time":1611630417,"name":"aplusb-demo-online-service","update_time":1611648368,"id":"aplusb-demo-online-service","hash_on":"vars","enable_websocket":false},"createdIndex":8875,"key":"\/apisix\/upstreams\/aplusb-demo-online-service"},"action":"get"}
```
Notice that the weight of `NodeA` is set to 100 and the weight of `NodeB` is
set to 0.
When `NodeB` is destroyed, I found that the API call fails. Error message in
`error.log` says:
```
parse_domain(): failed to parse domain: <NodeB>, error: server returned
error code: 3: name error...
```
Then I weed out the offline `NodeB`, the API call succeeds.
I'm confused. The weight of `NodeB` is set to 0, why this node still causes
a 5xx error? Maybe we need a document to explain this to other users.
### Environment
* apisix version (cmd: `apisix version`): 2.1
* OS (cmd: `uname -a`): Linux
* OpenResty / Nginx version (cmd: `nginx -V` or `openresty -V`):
openresty/1.19.3.1
* etcd version, if have (cmd: run `curl
http://127.0.0.1:9090/v1/server_info` to get the info from server-info API):
* apisix-dashboard version, if have:
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