> ## Documentation Index
> Fetch the complete documentation index at: https://docs.appsignal.com/llms.txt
> Use this file to discover all available pages before exploring further.

# DNS timeouts

## Affected components

* AppSignal for Ruby gem versions: `2.1.x` - `2.3.x` (later versions only partially affected, see [workarounds](#workaround))
* AppSignal for Elixir package versions: `0.10.x` - `1.3.x` (later versions only partially affected, see [workarounds](#workaround))
* Systems: In combination with hosts running [libc], not musl libc (Alpine Linux). macOS is unaffected.

## Description

In version `2.1.0` AppSignal switched to an agent built against the [musl libc][musl] implementation to [support Alpine Linux][blog-gem-2.1]. Adding support for Alpine Linux we switched our agent build over to musl libc. A DNS issue was [fixed in musl libc version `1.1.13`][musl-faq-dns], which we included in the next releases of AppSignal integrations.

In Ruby gem version `2.1.1` and Elixir package version `0.11.3` we also tried to fix the known ["ndots" DNS issue][musl-faq-dns] by hard-coding the DNS servers as a temporary solution. This caused problems with setups that use an private internal network that blocks outgoing DNS requests.

## Symptoms

* No data is being received by AppSignal after an upgrade of our integration to one of the affected versions.
* No data is being received by AppSignal after an infrastructure change.
* In our log file, `appsignal.log`, timeouts are being reported.
* The application's host is running a non-musl libc system, anything but Alpine Linux.
* The `/etc/resolv.conf` configuration file contains entries that contains more than four dots, e.g. `namespace.namespace.cluster.two.local`. This is true for systems that use [kubernetes] and similar systems for infrastructure management.
* The host's (private) network blocks outgoing DNS requests. You can test this by running `dig @8.8.8.8 NS push.appsignal.com` on the host.

## Solution

A complete fix was released in AppSignal for Ruby gem [version `2.4.0`](https://blog.appsignal.com/2017/10/31/ruby-gem-2-4.html) and AppSignal for Elixir package [version `1.4.0`](https://blog.appsignal.com/2017/11/02/elixir-package-1-4.html) by providing a separate musl-based build to musl systems. Non-musl systems will use a non-musl agent and extension build.

Upgrade to the latest version of AppSignal for the language your app uses.

## Workaround

These workaround are no longer necessary unless you're unable to upgrade to the latest AppSignal version for the language your app uses.

* The hardcoded DNS servers were reverted in AppSignal for Ruby gem version `2.2.0` and AppSignal for Elixir package `1.3.0`.
  This won't fix the musl libc "ndots" bug, but provides a configuration option for the DNS servers ([Ruby](/ruby/configuration/options#option-dns_servers) & [Elixir](/elixir/configuration/options#option-dns_servers)) if an application encounters into this problem. This allows for a (local) DNS server to be set manually if musl libc can't read the DNS configuration of the host.
* Allow outgoing DNS requests from within the private network for the machines that have AppSignal installed.

[blog-gem-2.1]: https://blog.appsignal.com/2017/01/31/gem-2-1.html

[libc]: https://www.gnu.org/software/libc/

[musl]: https://www.musl-libc.org/

[musl-faq-dns]: https://wiki.musl-libc.org/functional-differences-from-glibc.html#Name_Resolver/DNS

[kubernetes]: https://kubernetes.io/