Motivation:
DN resolution does not fall back to the "original name" lookup after search list is checked. This results in a failure to resolve any name (outside of search list) that has number of dots less than resolv.conf's ndots value (which, for example, is often the case in the context of Kubernetes where kubelet passes on resolv.conf containing "options ndots:5").
It also does not go through the search list in a situation described in resolv.conf man:
"The default for n[dots] is 1, meaning that if there are any dots in a name, the name will be tried first as an absolute name before any search list elements are appended to it."
Modifications:
DnsNameResolverContext::resolve was updated to match Go's https://github.com/golang/go/blob/release-branch.go1.9/src/net/dnsclient_unix.go#L338 logic.
Result:
DnsNameResolverContext::resolve will now try to resolve "original name" if search list yields no results when number of dots in the original name is less than resolv.conf's ndots value. It will also go through the search list in case "origin name" resolution fails and number of dots is equal or larger than resolv.conf's ndots value.
Motviation:
DnsNameResolverContext#followCname attempts to build a query to follow a CNAME, but puts the original hostname in the DnsQuery instead of the CNAME hostname. This will result in not following CNAME redirects correctly.
Result:
- DnsNameResolverContext#followCname should use the CNAME instead of the original hostname when building the DnsQuery
Result:
More correct handling of redirect queries.
Motivation:
Even if it's a super micro-optimization (most JVM could optimize such
cases in runtime), in theory (and according to some perf tests) it
may help a bit. It also makes a code more clear and allows you to
access such methods in the test scope directly, without instance of
the class.
Modifications:
Add 'static' modifier for all methods, where it possible. Mostly in
test scope.
Result:
Cleaner code with proper 'static' modifiers.
Motivation:
DnsCache (an interface) is coupled to DnsCacheEntry (a final class). This means that DnsCache implementations can't implement their own DnsCacheEntry objects if the default behavior isn't appropriate.
Modifications:
- DnsCacheEntry should be moved to DefaultDnsCache as it is an implementation detail
- DnsCache#cache(..) should return a new DnsCacheEntry
- The methods which from DnsCacheEntry that were used outside the scope of DefaultDnsCache should be moved into an interface
Result:
DnsCache is more extensible and not tightly coupled to a default implementation of DnsCacheEntry.
Motivation:
DnsNameResolverTest has been observed to timeout on the CI servers. We should increase the timeout from 5 seconds to 30 seconds.
Modifications:
- Increase timeout from 5 to 30 seconds.
Result:
Less false failures due to slower CI machines.
Motivation:
The DNS resolver may use default configuration inherited from the environment. This means the ndots value may change and result in test failure if the tests don't explicitly set the assumed value.
Modifications:
- Explicitly set ndots in resolver-dns unit tests so we don't fail if the environment overrides the search domain and ndots
Result:
Unit tests are less dependent upon the enviroment they run in.
Fixes https://github.com/netty/netty/issues/6966.
Motivation:
UnixResolverDnsServerAddressStreamProvider currently throws an exception if /etc/resolver exists but it empty. This shouldn't be an exception and can be tolerated as if there is no contribution from /etc/resolver.
Modifications:
- Treat /etc/resolver as present and empty the same as not being present
Result:
UnixResolverDnsServerAddressStreamProvider initialization can tolerate empty /etc/resolver directory.
Motivation:
InetSocketAddress#getHostName() may attempt a reverse lookup which may lead to test failures because the expected address will not match.
Modifications:
- Use InetSocketAddress#getHostString() which will not attempt any lookups and instead return the original String
Result:
UnixResolverDnsServerAddressStreamProviderTest is more reliable.
Motivation:
If there are multiple DNS servers to query Java's DNS resolver will attempt to resolve A and AAAA records in sequential order and will terminate with a failure once all DNS servers have been exhausted. Netty's DNS server will share the same DnsServerAddressStream for the different record types which may send the A question to the first host and the AAAA question to the second host. Netty's DNS resolution also may not progress to the next DNS server in all situations and doesn't have a means to know when resolution has completed.
Modifications:
- DnsServerAddressStream should support new methods to allow the same stream to be used to issue multiple queries (e.g. A and AAAA) against the same host.
- DnsServerAddressStream should support a method to determine when the stream will start to repeat, and therefore a failure can be returned.
- Introduce SequentialDnsServerAddressStreamProvider for sequential use cases
Result:
Fixes https://github.com/netty/netty/issues/6926.
Motivation:
ba80fbbe05 modified the UnknownHostException to not include the search domain if the DNS query failed, but this masks what DNS query actually failed. Have the full hostname (including the search domain) provides more visibility and may help diagnose a configuration error if queries are unexpectedly failing.
Modifications:
- Remove DnsNameResolverContext#pristineHostname
Result:
UnknownHostException is more accurate and reflect what hostname actually resulted in failure.
Motivation:
The DNS resolver supports search domains. However the ndots are not correctly enforced. The search domain should only be appended under the following scenario [1]:
> Resolver queries having fewer than ndots dots (default is 1) in them will be attempted using each component of the search path in turn until a match is found.
The DNS resolver current appends the search domains if ndots is 0 which should never happen (because no domain can have less than 0 dots).
[1] https://linux.die.net/man/5/resolv.conf
Modifications:
- Parse /etc/resolv.conf to get the default value for ndots on Unix platforms
- The search domain shouldn't be used if ndots is 0
- Avoid failing a promise to trigger the search domain queries in DnsNameResolverContext#resolve
Result:
More correct usage of search domains in the DNS resolver.
Fixes https://github.com/netty/netty/issues/6844.
Motivation:
UnixResolverDnsServerAddressStreamProvider allows the default name server address stream to be null, but there should always be a default stream to fall back to ([1] Search Strategy).
UnixResolverDnsServerAddressStreamProvider currently shuffles the names servers are multiple are present, but the defined behavior is to try them sequentially [2].
[1] Search Strategy Section - https://developer.apple.com/legacy/library/documentation/Darwin/Reference/ManPages/man5/resolver.5.html
[2] DESCRIPTION/nameserver Section - https://developer.apple.com/legacy/library/documentation/Darwin/Reference/ManPages/man5/resolver.5.html
Modifications:
- UnixResolverDnsServerAddressStreamProvider should always use the first file provided to derive the default domain server address stream. Currently if there are multiple domain names in the file identified by the first argument of the constructor then one will be selected at random.
- UnixResolverDnsServerAddressStreamProvider should return name servers sequentially.
- Reduce access level on some methods which don't have known use-cases externally.
Result:
Fixes https://github.com/netty/netty/issues/6736
Motivation:
IDN.toUnicode(...) removes trailing dots when used in Java7 while it not does on java8.
Modifications:
Check if we should test with the trailing dot removed or not.
Result:
Test pass on Java7 as well.
Motivation:
A single DNS query may follow many different paths through resolver-dns. The query may fail for various reasons related to the DNS protocol, general IO errors, it may be cancelled due to the query count being exceeded, or other reasons. A query may also result in other queries as we follow the DNS protocol (e.g. redirects, CNAME, etc...). It is currently impossible to collect information about the life cycle of an individual query though resolver-dns. This information may be valuable when considering which DNS servers are preferred over others.
Modifications:
- Introduce an interface which can provide visibility into all the potential outcomes of an individual DNS query
Result:
resolver-dns provides visibility into individual DNS queries which can be used to avoid poorly performing DNS servers.
Motivation:
DnsServerAddresses loads the default DNS servers used for DNS resolution in a static initialization block. This is subject to blocking and may cause unexpected delays. We can move this initialization to DefaultDnsServerAddressStreamProvider where it is more expected to load the JDK's default configuration.
Modifications:
- Move all the static initialization from DnsServerAddresses to DefaultDnsServerAddressStreamProvider
- Deprecate static methods in DnsServerAddresses which have moved to DefaultDnsServerAddressStreamProvider
- Remove usage of deprecated methods in DnsServerAddresses
Result:
Usage of JDK's blocking DNS resolver is not required to use resolver-dns.
Motivation:
Recently DnsServerAddressStreamProvider was introduced to allow control for each query as to which DNS server should be used for resolution to respect the local host's default DNS server configuration. However resolver-dns also accepts a stream of DNS servers to use by default, but this stream is not host name aware. This creates an ambiguity as to which method is used to determine the DNS server to user during resolution, and in which order. We can remove this ambiguity and provide a more general API by just supporting DnsServerAddressStreamProvider.
Modifications:
- Remove the fixed DnsServerAddresses and instead only accept a DnsServerAddressStreamProvider.
- Add utility methods to help use DnsServerAddressStreamProvider for a single entry, a list of entries, and get the default for the current machine.
Result:
Fixes https://github.com/netty/netty/issues/6573.
Motivation:
We have our own ThreadLocalRandom implementation to support older JDKs . That said we should prefer the JDK provided when running on JDK >= 7
Modification:
Using ThreadLocalRandom implementation of the JDK when possible.
Result:
Make use of JDK implementations when possible.
Motivation:
54c9ecf682 introduced a unit tests which attempted to exclude addresses which resolved to loop back addresses from an assert statement. This was done with a static check for localhost but depending on machine configuration it is possible for other interfaces to be resolved.
Modifications:
- Use InetAddress#isLoopbackAddress() instead of string match on localhost
Result:
DnsNameResolverTest#testNameServerCache is more reliable.
Motivation:
The JDK uses gethostbyname for blocking hostname resoltuion. gethostbyname can be configured on Unix systems according to [1][2]. This may impact the name server that is used to resolve particular domains or just override the default fall-back resolver. DnsNameResolver currently ignores these configuration files which means the default resolution behavior is different than the JDK. This may lead to unexpected resolution failures which succeed when using the JDK's resolver.
Modifications:
- Add an interface which can override what DnsServerAddressStream to use for a given hostname
- Provide a Unix specific implementation of this interface and implement [1][2]. Some elements may be ignored sortlist, timeout, etc...
Result:
DnsNameResolver behaves more like the JDK resolver by default.
[1] https://linux.die.net/man/5/resolver
[2] https://developer.apple.com/legacy/library/documentation/Darwin/Reference/ManPages/man5/resolver.5.html
Motivation:
HostsFileParser only retains the first address for each given hostname.
This is wrong, and it’s allowed to have both an IPv4 and an IPv6.
Modifications:
* Have `HostsFileParser` now return a `HostsFileEntries` that contains IPv4 entries and IPv6 entries
* Introduce `ResolvedAddressTypes` to describe resolved address types preferences
* Add a new `ResolvedAddressTypes` parameter to `HostsFileEntriesResolver::address` to account for address types preferences
* Change `DnsNameResolver` constructor to take a `ResolvedAddressTypes`, allowing for a null value that would use default
* Change `DnsNameResolverBuilder::resolvedAddressTypes` to take a `ResolvedAddressTypes`
* Make `DnsNameResolver::resolvedAddressTypes` return a `ResolvedAddressTypes`
* Add a static `DnsNameResolverBuilder::computeResolvedAddressTypes` to ease converting from `InternetProtocolFamily`
Result:
We now support hosts files that contains IPv4 and IPv6 pairs for a same
hostname.
Motivation:
a416b79 introduced a check for null or empty host name to be compatible with the JDK resolution. However the doResolve(String, Promise) method, and if the doResolve(String, DnsRecord[], Promise, DnsCache) method was overridden the empty/null hostname would not be correctly resolved.
Modifications:
- Move the empty/null host name check into the lowest level doResolve method in DnsNameResolver
- Remove the duplicate logic in InetNameResolver.java which can be bypassed anyways
Result:
By default (unless behavior is overridden) DnsNameResolver resolves null/empty host names to local host just like the JDK.
Motivation:
DnsNameResolver does not handle recursive DNS and so fails if you query a DNS server (for example a ROOT dns server) which provides the correct redirect for a domain.
Modification:
Add support for redirects (a.k.a. handling of AUTHORITY section').
Result:
Its now possible to use a DNS server that redirects.
Motivation:
DnsNameResolver will return the domain / host name as ascii code using punycode (https://tools.ietf.org/html/rfc3492). This is different to what the JDK does which always convert it to unicode. We should do the same by default but allow to also not do it.
Modifications:
- Add new builder method on DnsNameResolverBuilder which allow to disable / enable converting. Default is to convert just like the JDK does.
- Add unit tests for it.
Result:
DnsNameResolver and JDK impl behave the same way.
Motivation:
When an empty hostname is used in DnsNameResolver.resolve*(...) it will never notify the future / promise. The root cause is that we not correctly guard against errors of IDN.toASCII(...) which will throw an IllegalArgumentException when it can not parse its input. That said we should also handle an empty hostname the same way as the JDK does and just use "localhost" when this happens.
Modifications:
- If the try to resolve an empty hostname we use localhost
- Correctly guard against errors raised by IDN.toASCII(...) so we will always noify the future / promise
- Add unit test.
Result:
DnsNameResolver.resolve*(...) will always notify the future.
Motivation:
Currently Netty does not wrap socket connect, bind, or accept
operations in doPrivileged blocks. Nor does it wrap cases where a dns
lookup might happen.
This prevents an application utilizing the SecurityManager from
isolating SocketPermissions to Netty.
Modifications:
I have introduced a class (SocketUtils) that wraps operations
requiring SocketPermissions in doPrivileged blocks.
Result:
A user of Netty can grant SocketPermissions explicitly to the Netty
jar, without granting it to the rest of their application.
Motivation:
RFC7871 defines an extension which allows to request responses for a given subset.
Modifications:
- Add DnsOptPseudoRrRecord which can act as base class for extensions based on EDNS(0) as defined in RFC6891
- Add DnsOptEcsRecord to support the Client Subnet in DNS Queries extension
- Add tests
Result:
Client Subnet in DNS Queries extension is now supported.
Motivation:
When a hostname cannot be resolved, the message in the UnknownHostException mentions the hostname with the last attempted search domain appended, which is kind of confusing. I would prefer to see the original hostname supplied to the method in the exception.
Modifications:
Store the pristine hostname in the resolver context and use it to create the exception message instead of the hostname with search domain.
Add unit test to check that the exception does not mention the search domain.
Result:
The exception mentions the unmodified hostname in the message.
Motivation:
The ndots = 0 is a valid value for ndots, it means that when using a non dotted name, the resolution should first try using a search and if it fails then use subdomains. Currently it is not allowed. Docker compose uses this when wiring up containers as names have usually no dots inside.
Modification:
Modify DnsNameResolver to accept ndots = 0 and handle the case in the resolution procedure. In this case a direct search is done and then a fallback on the search path is performed.
Result:
The ndots = 0 case is implemented.
Motivation:
When resolving localhost on Windows where the hosts file does not contain a localhost entry by default, the resulting InetAddress object returned by the resolver does not have the hostname set so that getHostName returns the ip address 127.0.0.1. This behaviour is inconsistent with Windows where the hosts file does contain a localhost entry and with Linux in any case. It breaks at least some unit tests.
Modifications:
Create the LOCALHOST4 and LOCALHOST6 objects with hostname localhost in addition to the address.
Add unit test domain localhost to DnsNameResolverTest to check the resolution of localhost with ipv4 at least.
Result:
The resolver returns a InetAddress object for localhost with the hostname localhost in all cases.
Motivation:
The current DnsNameResolver does not support search domains resolution. Search domains resolution is supported out of the box by the java.net resolver, making the DnsNameResolver not able to be a drop in replacement for io.netty.resolver.DefaultNameResolver.
Modifications:
The DnsNameResolverContext resolution has been modified to resolve a list of search path first when it is configured so. The resolve method now uses the following algorithm:
if (hostname is absolute (start with dot) || no search domains) {
searchAsIs
} else {
if (numDots(name) >= ndots) {
searchAsIs
}
if (searchAsIs wasn't performed or failed) {
searchWithSearchDomainsSequenciallyUntilOneSucceeds
}
}
The DnsNameResolverBuilder provides configuration for the search domains and the ndots value. The default search domains value is configured with the OS search domains using the same native configuration the java.net resolver uses.
Result:
The DnsNameResolver performs search domains resolution when they are present.
Motivation:
If DnsNameResolver works with NoopDnsCache, IndexOutOfBoundsException will
be thrown.
Modifications:
Test if the result of DnsNameResolver.get(hostname) is empty before
accessing it's elements.
Related: #4771
Motivation:
A malicious or misconfigured DNS server can send the CNAME records that
resolve into each other, causing an unexpected infinite loop in
DnsNameResolverContext.onResponseCNAME().
Modifications:
- Remove the dereferenced CNAME from the alias map so that infinite loop
is impossible.
- Fix inspection warnings and typos in DnsNameResolverTest
Result:
Fixes#4771
Motivation:
As "getHostName" may do a reverse name lookup and return a host name based on the system configured name lookup service, testResolveIp may fail in some special environment. See #4720
Modifications:
Use getHostAddress instead of getHostName
Result:
testResolveIp works in all environments
Motivation:
On contrary to `DefaultNameResolver`, `DnsNameResolver` doesn't currently honor hosts file.
Modifications:
* Introduce `HostsFileParser` that parses `/etc/hosts` or `C:\Windows\system32\drivers\etc\hosts` depending on the platform
* Introduce `HostsFileEntriesResolver` that uses the former to resolve host names
* Make `DnsNameResolver` check his `HostsFileEntriesResolver` prior to trying to resolve names against the DNS server
* Introduce `DnsNameResolverBuilder` so we now have a builder for `DnsNameResolver`s
* Additionally introduce a `CompositeNameResolver` that takes several `NameResolver`s and tries to resolve names by delegating sequentially
* Change `DnsNameResolver.asAddressResolver` to return a composite and honor hosts file
Result:
Hosts file support when using `DnsNameResolver`.
Consistent behavior with JDK implementation.
Motivation:
As discussed in #4529, NameResolver design shouldn't be resolving SocketAddresses (or String name + port) and return InetSocketAddresses. It should resolve String names and return InetAddresses.
This SocketAddress to InetSocketAddresses resolution is actually a different concern, used by Bootstrap.
Modifications:
Extract SocketAddress to InetSocketAddresses resolution concern to a new class hierarchy named AddressResolver.
These AddressResolvers delegate to NameResolvers.
Result:
Better separation of concerns.
Note that new AddressResolvers generate a bit more allocations because of the intermediate Promise and List<InetAddress>.
Motivation:
As relaying on external DNS Server can result to test-failures we should better use a mock DNS Server for the dns tests.
Modifications:
- Refactor the DnsNameResolverTest to use a mock DNS Server which is using apacheds.
- Allow to disable adding an opt resources as some servers not support it.
Result:
More stable testsuite.
Motivation:
Some DNS servers in DnsNameResolverTest are outdated and some of them
returns NoError for non-existent domains.
Modifications:
- Update the DNS server list from http://meo.ws/dnsrec.php again
- Update the web-scraper script
Result:
DnsNameResolverTest.testNegativeTtl() should not fail anymore.
Motivation:
DNS lookups in DnsNameResolverTest can take longer than expected due to
retries. The hard limit of 5 seconds is being applied to
testNegativeTtl(), making the first uncached lookup cause a timeout.
Modifications:
Do not use JUnit's Timeout annotation but implement simple timeout
mechanism that apples only to cached lookups.
Result:
testNegativeTtl() should not fail when an initial negative lookup
requires a retry.
Motivation:
- DNS lookup sometimes hang because it does not call
tryToFinishResolve()
- Comodo Secure DNS handles negative lookup incorrectly.
Modifications:
- Add missing tryToFinishResolve()
- Remove Comodo Secure DNS servers from the list
Result
- DNS lookup does not hang on non-existent domain names
- More reliable DnsNameResolverTest
Related: #4065
Motivation:
DnsNameResolver was using a special Iterable/Iterator implementation
that yields an infinite stream of DNS server addresses. However, this
seems to cause confusion.
Modifications:
- Make DnsServerAddresses an abstract class with an abstract stream()
method that returns DnsServerAddressStream
- Add DnsServerAddressStream that yields DNS server address infinitely
- Remove DnsServerResolver(Group) constructors that accept only a single
server address, which wasn't very useful in practice
- Extract the DnsServerAddresses implementations to top level
- DnsServerAddresses.defaultAddresses() now returns DnsServerAddresses.
- Add DnsServerAddresses.defaultAddressList() instead
Result:
Less confusion and more explicitness
Motivation:
DNS servers seem to reply with ServFail(2) response code when it is
busy.
Modifications:
- Retry when response code is ServFail instead of failing the test
- Try all DNS servers instead of retrying twice only
Result:
testQueryMx() is less likely to fail due to public DNS server problems
Related issues:
- #3971
- #3973
- #3976
- #4035
Motivation:
1. Previously, DnsNameResolver.query() retried the request query by its
own. It prevents a user from deciding when to retry or stop. It is also
impossible to get the response object whose code is not NOERROR.
2. NameResolver does not have an operation that resolves a host name
into multiple addresses, like InetAddress.getAllByName()
Modifications:
- Changes related with DnsNameResolver.query()
- Make query() not retry
- Move the retry logic to DnsNameResolver.resolve() instead.
- Make query() fail the promise only when I/O error occurred or it
failed to get a response
- Add DnsNameResolverException and use it when query() fails so that
the resolver can give more information about the failure
- query() does not cache anymore.
- Changes related with NameResolver.resolveAll()
- Add NameResolver.resolveAll()
- Add SimpleNameResolver.doResolveAll()
- Changes related with DnsNameResolver.resolve() and resolveAll()
- Make DnsNameResolveContext abstract so that DnsNameResolver can
decide to get single or multiple addresses from it
- Re-implement cache so that the cache works for resolve() and
resolveAll()
- Add 'traceEnabled' property to enable/disable trace information
- Miscellaneous changes
- Use ObjectUtil.checkNotNull() wherever possible
- Add InternetProtocolFamily.addressType() to remove repetitive
switch-case blocks in DnsNameResolver(Context)
- Do not raise an exception when decoding a truncated DNS response
Result:
- Full control over query()
- A user can now retrieve all addresses via (Dns)NameResolver.resolveAll()
- DNS cache works only for resolve() and resolveAll() now.
Motivation:
DnsResolver.resolve(...) fails when an InetSocketAddress is used that was constructed of an ipaddress string.
Modifications:
Don't try to lookup when the InetSocketAddress was constructed via an ipaddress.
Result:
DnsResolver.resolve(...) works in all cases.
Motivation:
There are various known issues in netty-codec-dns:
- Message types are not interfaces, which can make it difficult for a
user to implement his/her own message implementation.
- Some class names and field names do not match with the terms in the
RFC.
- The support for decoding a DNS record was limited. A user had to
encode and decode by him/herself.
- The separation of DnsHeader from DnsMessage was unnecessary, although
it is fine conceptually.
- Buffer leak caused by DnsMessage was difficult to analyze, because the
leak detector tracks down the underlying ByteBuf rather than the
DnsMessage itself.
- DnsMessage assumes DNS-over-UDP.
- To send an EDNS message, a user have to create a new DNS record class
instance unnecessarily.
Modifications:
- Make all message types interfaces and add default implementations
- Rename some classes, properties, and constants to match the RFCs
- DnsResource -> DnsRecord
- DnsType -> DnsRecordType
- and many more
- Remove DnsClass and use an integer to support EDNS better
- Add DnsRecordEncoder/DnsRecordDecoder and their default
implementations
- DnsRecord does not require RDATA to be ByteBuf anymore.
- Add DnsRawRecord as the catch-all record type
- Merge DnsHeader into DnsMessage
- Make ResourceLeakDetector track AbstractDnsMessage
- Remove DnsMessage.sender/recipient properties
- Wrap DnsMessage with AddressedEnvelope
- Add DatagramDnsQuest and DatagramDnsResponse for ease of use
- Rename DnsQueryEncoder to DatagramDnsQueryEncoder
- Rename DnsResponseDecoder to DatagramDnsResponseDecoder
- Miscellaneous changes
- Add StringUtil.TAB
Result:
- Cleaner APi
- Can support DNS-over-TCP more easily in the future
- Reduced memory footprint in the default DnsQuery/Response
implementations
- Better leak tracking for DnsMessages
- Possibility to introduce new DnsRecord types in the future and provide
full record encoder/decoder implementation.
- No unnecessary instantiation for an EDNS pseudo resource record
Motivation:
DnsNameResolver.testResolveA() tests if the cache works as well as the usual DNS protocol test. To ensure the result from the cache is identical to the result without cache, it compares the two Maps which contain the result of cached/uncached resolution. The comparison of two Maps yields an expected behavior, but the output of the comparison on failure is often unreadable due to its long length.
Modifications:
Compare entry-by-entry for more comprehensible test failure output
Result:
When failure occurs, it's easier to see which domain was the cause of the problem.
Motivation:
So far, we relied on the domain name resolution mechanism provided by
JDK. It served its purpose very well, but had the following
shortcomings:
- Domain name resolution is performed in a blocking manner.
This becomes a problem when a user has to connect to thousands of
different hosts. e.g. web crawlers
- It is impossible to employ an alternative cache/retry policy.
e.g. lower/upper bound in TTL, round-robin
- It is impossible to employ an alternative name resolution mechanism.
e.g. Zookeeper-based name resolver
Modification:
- Add the resolver API in the new module: netty-resolver
- Implement the DNS-based resolver: netty-resolver-dns
.. which uses netty-codec-dns
- Make ChannelFactory reusable because it's now used by
io.netty.bootstrap, io.netty.resolver.dns, and potentially by other
modules in the future
- Move ChannelFactory from io.netty.bootstrap to io.netty.channel
- Deprecate the old ChannelFactory
- Add ReflectiveChannelFactory
Result:
It is trivial to resolve a large number of domain names asynchronously.
