MIME-Version: 1.0
From: Banibrata Dutta <banibrata.dutta@gmail.com>
Date: Thu, 4 Mar 2021 02:41:08 +0530
Message-ID: <CALODqpruOKWhKhs8gShNac3T3=H7SDzdMOpo45zS00f-FCcQ1w@mail.gmail.com>
Subject: Sporadic, unpredictable docker / docker-compose (on Alpine 3.13)
 issues with DNS name resolution
To: ~alpine/users@lists.alpinelinux.org
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Hi Folks,

Have been using docker and docker-compose inside Virtualbox VMs running
Alpine 3.13 guestOS, on a Windows 10 Professional host. The Alpine Guest
has 2 vCPUs, 4GB vRAM, and even when all containers are running the RAM
usage remains below 1GB.

   - Docker version 20.10.3, build 48d30b5b32e99c932b4ea3edca74353feddd83ff
   - docker-compose version 1.27.4, build unknown

I use 2 docker-compose .yml files to bring up, 2 set of containers. First
.yml file brings up Telgraf, InfluxDB, Grafana containers based on images
from DockerHub. The second .yml brings up a POJO-server (Java) with
application and another 3 tester/simulators.They all share a dedicated
network =E2=80=98mynet=E2=80=99 (using bridged driver). The above setup see=
ms to work
perfectly at times. For example:

   -

   Sometimes , containers don=E2=80=99t seem to get hostname assigned (i.e.=
 the
   mnemonic container-id is set as hostname, as is default) while at other
   times specific hostname is indeed assigned.
   -

   Then, for a few containers (not all), the inter-container DNS/name
   resolution doesn=E2=80=99t seem to work, but at the same time few other =
containers
   have perfectly working inter-container DNS/name resolution. When
   inter-container DNS resolution does-not, if I log into the container
   runtime using =E2=80=98docker exec -it bash=E2=80=99, and try to do 'pin=
g ', I get the
   following error:
   *ping: somehostname: Temporary failure in name resolution*
   -

   Sometimes, some containers (not all) require the "service: > hostname: "
   declaration in the docker-compose .yml file to get specific hostname
   assigned to the container, but for other containers at other times, that
   declaration is not needed, and only the =E2=80=9Ccontainer_name=E2=80=9D=
 declaration is
   enough (in .yml file) to have specific hostname for that container !!

Wondering if anyone can help figure out why is the behaviour erratic ? What
can I do to fix it ? Is this an issue with Docker only on Alpine ?

Thanks in anticipation.
regards,
BD

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<div dir=3D"ltr">
<div class=3D"gmail-cooked"><p>Hi Folks,</p>
<p>Have been using docker and docker-compose inside Virtualbox VMs running =
Alpine 3.13 guestOS, on a Windows 10 Professional host. The Alpine Guest ha=
s 2 vCPUs, 4GB vRAM, and even when all containers are running the RAM usage=
 remains below 1GB.<br></p>
<ul><li>Docker version 20.10.3, build 48d30b5b32e99c932b4ea3edca74353feddd8=
3ff</li><li>docker-compose version 1.27.4, build unknown</li></ul>
<p>I use 2 docker-compose .yml files to bring up, 2 set of containers.=20
First .yml file brings up Telgraf, InfluxDB, Grafana containers based on
 images from DockerHub. The second .yml brings up a POJO-server (Java)=20
with application and another 3 tester/simulators.They all share a=20
dedicated network =E2=80=98mynet=E2=80=99 (using bridged driver). The above=
 setup seems=20
to work perfectly at times. For example:</p>
<ul><li>
<p>Sometimes , containers don=E2=80=99t seem to get hostname assigned (i.e.=
 the=20
mnemonic container-id is set as hostname, as is default) while at other=20
times specific hostname is indeed assigned.</p>
</li><li>
<p>Then, for a few containers (not all), the inter-container DNS/name=20
resolution doesn=E2=80=99t seem to work, but at the same time few other=20
containers have perfectly working inter-container DNS/name resolution.=20
When inter-container DNS resolution does-not, if I log into the=20
container runtime using =E2=80=98docker exec -it  bash=E2=80=99, and try to=
 do &#39;ping &#39;, I
 get the following error:<br>
<i>ping: somehostname: Temporary failure in name resolution</i></p>
</li><li>
<p>Sometimes, some containers (not all) require the &quot;service: &gt;=20
hostname: &quot; declaration in the docker-compose .yml file to get specifi=
c=20
hostname assigned to the container, but for other containers at other=20
times, that declaration is not needed, and only the =E2=80=9Ccontainer_name=
=E2=80=9D=20
declaration is enough (in .yml file) to have specific hostname for that=20
container !!</p>
</li></ul>
<p>Wondering if anyone can help figure out why is the behaviour erratic ? W=
hat can I do to fix it ? Is this an issue with Docker only on Alpine ?<br><=
/p>
<p>Thanks in anticipation.</p></div><div>regards,</div><div>BD<br></div></d=
iv>

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