404 Multi Hop Cycle Issue

[amoghyermalkar123]

I have a remap on a child node that looks like this -

map http://something.some.com/ http://something.some.com/

On parent node, the respective mapping is

map http://something.some.com/ http://originserver.com/

I currently have only one parent configured in parent.config, so if for some reason the parent server fails,
ATS tries to DNS resolve something.some.com - this is problematic for me.

something.some.com when DNS resolved, points to the child server itself. This results in a 404 Multi Hop.

How can I avoid this?

[amoghyermalkar123]

@bryancall please help.

[amoghyermalkar123]

My goal is to only use remap as an outbound request formation logic and use parent.config to route to parent.
If parent is unreachable it should just send 4xx. Not try to DNS resolve the outbound host header.

[jrushford]

@amoghyermalkar123 Try this on the reverse proxy child node.
remap.config:

map http://something.some.com/ http://originserver.com/

parent.config:

dest_domain=originserver.com port=80 parent="parent.some.com:80" round_robin=false go_direct=true

If the parent fails, it'll retry by going to the origin directly. If you don't want your child to go directly to the origin, then change go_direct=false. In this case, when the parent fails, you'll get a 502 back.

Your parent.som.com is a forward proxy you don't really need the remap.config unless you require remap in records.config. If you require the remap then your remap.config on the parent is:

map http://originserver.com/ http://originserver.com/

Let me know if this works or not, I'll try to help you out.

[amoghyermalkar123]

Hi @jrushford , your mappings helped alot, I am indeed not seeing multi-hop cycle anymore with the following configurations : (although I might need to test a bit more)

child remap:
map http://something.some.com/ http://something.some.com/

child parent:
dest_domain=something.some.com method=get port=443 parent="some_ip_address:443" scheme=https round_robin=strict go_direct=false

========================

parent remap:
map http://something.some.com/ http://originserver.com/

========================

As you said, I am seeing 502 Next hop connection failure.
I have a few follow up questions regarding this approach :

1. When a parent gives a child 5xx, child will mark parent as down, correct?
2. if 1. is true, how do we know when the child will mark the parent up? (question stands even if mark down/up is per remap)
3. Do you have any pointers on the updated configs I have attached? Anything I might miss, something I should be aware of?

Edit:
4) Also can I get a few examples about the usage of url_regex in parent.config instead of dest_domain? I have quite a few domains that follow a pattern and have the same origin, so it would be better to have one line in parent.config under a regex instead of one for each domain.
I tried doing url_regex=pattern* but it didn't seem to work as multi-hop cycle kept occuring. But when I use dest_domain I get expected result i.e. 502

[jrushford]

@amoghyermalkar123 Here are my replies

1. Yes, the child will mark the parent down for a connection failure but not if the parent sends a 502 response to the child. There are some config options in parent.config that you can use to have the child retry a 502 response from a parent using a different parent. There is also this configuration parameter to be aware of for markdowns:
   proxy.config.http.parent_proxy.fail_threshold

2. proxy.config.http.parent_proxy.retry_time is basically sliding retry window setting. Once the retry_time expires, a down parent is selected and is retried. If the transaction is successful, the parent is marked up. If the connection fails, the parent is left down and the retry time is set again.

3. Your configs look good. The only thing I can think of is to just look through the Parent Proxy Configuration settings, the parent.config, and Hierarchical Caching

In a future release, parent.config will probably be deprecated. In ATS 9.1 and preferably 9.2, You can use strategies.yaml as this will replace parent.config

I'm on the ATS slack channel and you can always email the user list or myself directly, jrushford@apache.org

[amoghyermalkar123]

@jrushford I really appreciate your help, thanks alot !

Have been testing, and haven't been seeing any multi-hops since, closing this issue.