etcdmain: better logging when user forget to set initial flags #3556

xiang90 · 2015-09-18T22:19:27Z

Now it will log as if you forgot to set both --initial-cluster and --discovery and the configuration does not match.

2015-09-18 15:19:16.721741 I | etcdmain: advertise URLs of "default" do not match in --initial-advertise-peer-urls [http://example.com:1234] and --initial-cluster [http://localhost:2380 http://localhost:7001]
2015-09-18 15:19:16.721746 I | etcdmain: forgot to set --initial-cluster flag?
2015-09-18 15:19:16.721754 I | etcdmain: if you want to use discovery service, please set --discovery flag.

yichengq · 2015-09-18T22:33:04Z

etcdmain/etcd.go

@@ -146,6 +147,19 @@ func Main() {
 			plog.Errorf("please check (cURL) the discovery token for more information.")
 			plog.Errorf("please do not reuse the discovery token and generate a new one to bootstrap the cluster.")
 		default:
+			if strings.Contains(err.Error(), "match") && strings.Contains(err.Error(), "--initial-cluster") {


does this deserve to be a specific error?

we have variables in this error. i would say no.

I see no better way to handle it. Let us do it in this method.

unless when we decide to construct ALL specific errors in etcdmain.

yichengq · 2015-09-18T22:40:36Z

LGTM. defer to @crawford

crawford · 2015-09-18T22:45:06Z

I still don't understand that original error. Can we fix that?

yichengq · 2015-09-18T22:53:13Z

@crawford xiang reinvents the log for the original error to be:

2015-09-18 15:19:16.721741 I | etcdmain: advertise URLs of "default" do not match in --initial-advertise-peer-urls [http://example.com:1234] and --initial-cluster [http://localhost:2380 http://localhost:7001]
2015-09-18 15:19:16.721746 I | etcdmain: forgot to set --initial-cluster flag?
2015-09-18 15:19:16.721754 I | etcdmain: if you want to use discovery service, please set --discovery flag.

Which part makes you confused?

xiang90 · 2015-09-18T23:25:38Z

@crawford I think the original error logging is clear enough, but did not give you a hint of how to fix it. It simply says the two flags you give to etcd does not match with each other.

crawford · 2015-09-21T01:03:45Z

As a user, I'm telling you that the error is not clear enough.

xiang90 · 2015-09-21T01:42:53Z

@crawford What do you expect to see? Or why do not think it is not clear enough after providing you all the hints?

crawford · 2015-09-21T02:33:43Z

I would rather us fix the original message instead of adding more details. Maybe something like "no initial cluster or discovery URL provided".

xiang90 · 2015-09-21T02:45:25Z

@crawford

First, the error message should tell you what the error is, rather than finding the cause of the error. The fact is that the two flags does not match with each other. We can make the wording better or providing details based on other context, but not change the error. That is why we add the details.

Second, your suggestion is not good. We should not try to hide an error message by providing one possible cause. There are other cases that can cause the error.

Also, can you tell me why adding the details is not good enough? It seems that the detailed message after the error message provides what you want based on your reply.

crawford · 2015-09-21T02:59:51Z

First, the error message should tell you what the error is, rather than finding the cause of the error.

Agreed, but I do not understand the error message. I don't need my hand held, I just need to be able to comprehend the message.

We can make the wording better or providing details based on other context, but not change the error.

You can rephrase the original error so that it gives some hint as to how the user got there in the first place. As it exists, one must understand the etcd codebase in order to interpret this error. That's not good.

Second, your suggestion is not good. We should not try to hide an error message by providing one possible cause. There are other cases that can cause the error.

Well, this is good to know. You know all of the cases; you come up with a better message.

Also, can you tell me why adding the details is not good enough? It seems that the detailed message after the error message provides what you want based on your reply.

Because instead of fixing the root cause, you've thrown a band-aid over it. I still cannot parse that original error message.

xiang90 · 2015-09-21T03:09:09Z

Because instead of fixing the root cause, you've thrown a band-aid over it.

OK. Let's try to fix this. I would love to fix root cause.

Let me explain the error in a verbose english. You can help to make it shorter. As someone who is very familiar with etcd, I think I am not the best person to shorten the error message.

To configure a local etcd, you need to set a flag to advertise its own peer urls to others. So other peers can use it to reach the local member. That is called --advertise-peer-urls.

To configure a static cluster, you need to set a to list the cluster members and their advertise-peer-urls including itself's. This flag is called --initial-cluster

So you can know that you will repeat the peer-url of the local member twice. One in the --advertise-peer-url flag and the other one in the --initial-cluster flag. If they do not match with each other, then you got an error

 advertise URLs of "default" do not match in --initial-advertise-peer-urls [http://example.com:1234] and --initial-cluster [http://localhost:2380 http://localhost:7001]

You might think that: you can simply remove the duplication. However, we will not. The reason is that we do want the users to repeat this important cluster-wide setting. We do not want one of them to overwrite the other one and we want each member to have exact same initial-cluster.

xiang90 · 2015-09-21T03:15:21Z

@crawford

With all these explanation, I still cannot think a better error message than simply telling the fact that the two flags do not match.

Well, this is good to know. You know all of the cases; you come up with a better message.

Again, I will not change the error message to explain the causes and you agreed on that. If we cannot come up with a better error message. I would rather keep the explanation here.

polvi · 2015-09-21T03:46:13Z

working:

$ etcd --name=foo --initial-advertise-peer-urls=http://localhost:2381 --initial-cluster='foo=http://localhost:2381'
...

Failure 1 (changing name=foo to name=default):

$ etcd --name=default --initial-advertise-peer-urls=http://localhost:2381 --initial-cluster='foo=http://localhost:2381'
....
2015-09-20 20:43:32.857996 C | etcdmain: couldn't find local name "default" in the initial cluster configuration

Failure 2 (changing advertise-peer-urls to be one that is not part of initial-cluster):

$ etcd --name=foo --initial-advertise-peer-urls=http://localhost:9000 --initial-cluster='foo=http://localhost:2381'
...
2015-09-20 20:44:56.765504 C | etcdmain: advertise URLs of "foo" do not match in --initial-advertise-peer-urls [http://localhost:9000] and --initial-cluster [http://localhost:2381]

polvi · 2015-09-21T03:48:36Z

With that it feels like the right error for "failure 2" above is:

"--initial-cluster must include foo=http://localhost:9000"

xiang90 · 2015-09-21T04:00:27Z

@polvi Right. That is another way to explain the mismatch. However, we are not sure if the information provided in --initial-advertise-peer-urls is correct or --initial-cluster is correct.

For example, when user forget to set --initial-advertise-peer-urls

etcd --name=foo --initial-cluster='foo=http://localhost:9999'

We will print out that --initial-cluster must include foo=http://localhost:2380, which is equally confusing in my opinion. They do not even know where 2380 comes from.

xiang90 · 2015-09-21T04:03:22Z

@polvi Or we can give them a priority when returning the error. If mismatch is caused by unset, complaints the unset. If it is a really mismatch (both set), complaints the initial-cluster.

/cc @crawford What do you think?

polvi · 2015-09-21T04:10:06Z

@crawford does this make sense to you at all?

$ etcd --name=foo --initial-cluster='foo=http://localhost:9000,foo=http://localhost:1000'
...
--initial-cluster must include "foo=http://localhost:2380,foo=http://localhost:7001" given --initial-advertise-peer-urls=http://localhost:2380,http://localhost:7001

crawford · 2015-09-21T17:35:43Z

@polvi yeah, that makes much more sense.

xiang90 · 2015-09-21T17:45:16Z

@crawford OK. We rephrased the original mismatch error as @polvi suggested.

etcdmain: better logging when user forget to set initial flags

polvi · 2015-09-21T19:35:57Z

Based on that commit it looks like it does not do the right thing. Could you run the code path with multiple advertise-urls and print the resulting message?

xiang90 · 2015-09-21T20:05:31Z

@polvi
Here is the result with multiple advertise-urls

etcdmain: --initial-cluster must include default=[http://example.com:1234 http://example.com:2345] given --initial-advertise-peer-urls=[http://example.com:1234 http://example.com:2345]

You want the error message to suggest the format that you can paste into the flag?

yichengq reviewed Sep 18, 2015
View reviewed changes

etcdmain: better logging when user forget to set initial flags

3b70bf8

xiang90 force-pushed the better_error_logging branch from 61834a5 to 3b70bf8 Compare September 21, 2015 17:43

xiang90 added a commit that referenced this pull request Sep 21, 2015

Merge pull request #3556 from xiang90/better_error_logging

6188933

etcdmain: better logging when user forget to set initial flags

xiang90 merged commit 6188933 into etcd-io:master Sep 21, 2015

xiang90 deleted the better_error_logging branch September 21, 2015 17:52

xiang90 added the backport/v3.3 label Oct 15, 2015

gyuho removed the backport/v3.3 label Nov 22, 2017

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etcdmain: better logging when user forget to set initial flags #3556

etcdmain: better logging when user forget to set initial flags #3556

xiang90 commented Sep 18, 2015

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etcdmain: better logging when user forget to set initial flags #3556

etcdmain: better logging when user forget to set initial flags #3556

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