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From John Omernik <j...@omernik.com>
Subject Re: Apache Drill High Availability using HAproxy
Date Mon, 27 Aug 2018 13:22:57 GMT
This is a great topic, that I have run into running Drill on Apache Mesos
due to each of my bits having essentially a DNS load balancer. (One DNS
Name, multiple Drill bits IPs assigned to them).   That said, I've run into
a few issues and have a few workarounds. Note, I am talking about the REST
API here, not the other interfaces, I am not sure how that would work,
(perhaps the same)

So the best way, if you are using HAProxy, is to use sticky connections.
Essentially, when a user connects to HA PRoxy, the connection to the
backend Drillbit will stay sticky there until a timeout period or the
session is closed.  This should allow you to ensure the best user exp,
while keeping HA.  I am not sure how HAProxy balances things, however, with
a decent Drill cluster size, it shouldn't be an issue.

I didn't have HAProxy setup, and so what I did in my jupyter_drill module (
https://github.com/johnomernik/jupyter_drill) is at the application level,
prior connecting to Drill, I did a DNS lookup and grabbed the first IP
returned. Then I directly connected to that drill bit, for the the duration
of the session. It's not perfect, and I have not tested this at scale, but
it has worked on a small scale. I even used some python requests module
magic to use use the host name in the SSL verification even though I am
connecting by IP.

So a few options, if you already are looking at HAProxy, checking into the
sticky connections.


On Mon, Aug 20, 2018 at 1:01 PM, Paul Rogers <par0328@yahoo.com.invalid>

> Hi Satish,
> You did not say if you are using HAProxy for the RESTful API or the native
> Drill RPC (as used by the Drill client, JDBC and ODBC.)
> To understand the use of proxies and load balancers, it is helpful to
> remember that Drill is a stateful SQL engine. Drill encourages the use of
> many stateful commands such as USE, CTTAS, and ALTER SESSION.
> Session state is lost when connecting to a new Drillbit, or reconnecting
> to the same Drillbit. Thus, a query that runs fine before the reconnect can
> fail afterwards.
> This issue is not unique to Drill; it is a common constraint of all
> old-school SQL engines.
> If state were not an issue, then the Drill client itself could handle HA.
> The client is given a list of ZK nodes. The client, on encountering a
> disconnect, could ask ZK for a new node and reconnect. Since ZK is HA, the
> client can also recover from a ZK node failure by trying another.
> We discussed this client-based HA approach multiple times, but each time,
> the SQL state has been a show-stopper.
> In short, the issue is not whether to use HAProxy to solve the problem;
> Drill can do it internally in the client. The issue is how to handle
> session state.
> A possible solution would be to store user session state in ZK so that we
> could re-establish the same logical session after a physical reconnection.
> In particular a unique session ID could be used to key connections to
> session state in ZK.
> Making this change would be a good contributor project: it involves
> detailed knowledge of how the Drill session and ZK state work, but is
> pretty isolated to just those specific areas.
> Thanks,
> - Paul
>     On Monday, August 20, 2018, 8:26:09 AM PDT, drill <
> ganesh.satish34@gmail.com> wrote:
>  Hi Team,
> Good Evening . I am Satish working as big data developer. I need your help
> regarding Drill high availability usinh Ha proxy load balancer.
> Is Apache drill supports High availability if yes please let me know the
> process.
> -Thanks,
> Satish
> Sent from Mail for Windows 10

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