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Created Load Balancing Options (markdown)

B00ze64 2018-04-07 01:26:27 -04:00
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# Load Balancing
`DNSCrypt-Proxy` comes with a load balancing algorithm. It will send consecutive DNS queries to different DNS servers randomly chosen from a sorted (fastest to slowest) set of a chosen size. The size of that set is what you can chose in the configuration file with the `lb_strategy =` parameter. A server will be chosen randomly among the N fastest servers in your list of servers (or if you are not specifically choosing servers with the `server_names =` parameter, among the N fastest servers from all servers that match your requirements.)
## How The List Of Servers Is Populated
When `DNSCrypt-Proxy`:
* Starts
* Each time the server certificates (for DNSCrypt servers) are retrieved/validated (every `cert_refresh_delay` minutes)
* Each time the list of servers is retrieved (every `refresh_delay` hours)
It calculates an initial RTT (Round-Trip Time) estimation for each resolver (for DoH servers, two initial test queries are made). This list is then sorted from fastest to slowest resolver.
## How The Servers Are Sorted
`DNSCrypt-Proxy` keeps the list of servers sorted at all times.
Each time a query is made to a server, the time it takes is used to adjust how fast `DNSCrypt-Proxy` thinks that the server is, using an exponentially weighted moving average. If the newly adjusted RTT of the resolver that was just used happens to be bigger (slower) than a randomly chosen candidate from the list of all servers, then these entries are swapped.
Over time, every server that is queried is compared with all the other servers and the list is kept sorted without actually having to sort it after every query. Slow servers will probably never compare favorably with the fast servers and will remain at the bottom of the list. Since response times vary appreciably even for the same server, especially since DNS servers need to query other servers to resolve domains when they are not in the cache, the servers at the top of the list might move around as time goes by.
## Your Load Balancing Options
So the servers are sorted from quickest to slowest. The load balancing is done using that list. You have a choice of 4 different ranges/sets from which to chose the server that will next be queried. The server is chosen randomly inside that set. The 4 possible values of the `lb_strategy =` parameter are:
* **fastest** (always pick the one fastest server in the list)
* **p2** (randomly chose between the top 2 fastest servers)
* **ph** (randomly chose between the top fastest half of all servers)
* **random** (just pick any random server from the list)
The default strategy is **p2** so `DNSCrypt-Proxy` will pick one of the two fastest servers. It will compare how fast that server was with a randomly chosen server and if that random server is faster, the random server will move up. The same is true for all strategies - random servers will move up in the list when they are faster than the server that was just queried.
## Some Remarks
If you enable logging and have a look at the `DNSCrypt-Proxy` log, you will see the response times of all your servers when the proxy starts. You should notice that only a few servers are very fast for you, with the majority being appreciably slower. What this means is that if you have a relatively large list of random server from around the world, and you chose the **ph** strategy, some of your queries will probably end-up using slower servers; **p2** is probably the best strategy to use.
# [Configuring server sources](Configuration-Sources)