nginx: calculation of server_names_hash_bucket_size not right

[justinsb]

The calculation of server_names_hash_bucket_size underestimates the required size.

With a long name (49 characters) I hit:

2017/04/19 02:01:08 [emerg] 28#28: could not build server_names_hash, you should increase server_names_hash_bucket_size: 64
nginx: [emerg] could not build server_names_hash, you should increase server_names_hash_bucket_size: 64
nginx: configuration file /tmp/nginx-cfg540721084 test failed

I confirmed in that temp file that server_names_hash_bucket_size is indeed set to 64.

Here is the relevant code:
https://github.com/nginx/nginx/blob/master/src/core/ngx_hash.c#L269

The correct calculation is NGX_HASH_ELT_SIZE(&names[n]) + sizeof(void *)

where NGX_HASH_ELT_SIZE(name) = (sizeof(void *) + ngx_align((name)->key.len + 2, sizeof(void *)))

So for us, assuming 64 bit, we want to do

8 + 8 + align8(len(s) + 2)

My 49 characters therefore, is 16 + align8(51) = 16 + 56 = 72 (and of course we then have to round up to the next power of 2, i.e. 128)

[justinsb]

(Working on a fix now)

[aledbf]

@justinsb I changed this a couple of days ago #607

[justinsb]

@aledbf right, but I think there's some extra nginx padding in the hash table that isn't accounted for. This is just on the length (i.e. key-size) as well - I haven't hit the total hash table size yet.

If in doubt, try creating an ingress with a host with 49 characters e.g.

minimal-ruby-app-staging.useast1a.k8s.example.com