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	for alpine-user@lists.alpinelinux.org; Wed, 03 Apr 2019 17:48:55 +0200
Subject: Re: [alpine-user] APK hangs on some packages
Cc: alpine-user@lists.alpinelinux.org
References: <bba9404b-2e6c-6d76-6fe1-256d393cc181@iceity.de>
 <20190403155340.7b4df67e@ncopa-macbook.copa.dup.pw>
From: Tristan Kohl <tristan@iceity.de>
Message-ID: <241e1a68-f52c-66bb-4443-b26d4b0b1c01@iceity.de>
Date: Wed, 3 Apr 2019 17:48:55 +0200
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Thanks for your suggestion. I ran mtu on both of my machines and inside
alpine containers, this is what I got in all instances (calling Alpine
CDN and my router):

#> mtu -d dl-cdn.alpinelinux.org
>From 151.101.112.249: icmp_seq=1 bytes=8
>From 151.101.112.249: icmp_seq=2 bytes=1480
1500

Looks to me as they all have the same value, to be honest I never heard
of MTU before (networking is like black magic to me) so I have no idea
what to do here. Will try to find some lecture about that topic. Also I
can not find clamp-mss in Alpine's repository.

Cheers,

Tristan


On 03.04.19 16:53, Natanael Copa wrote:
> On Wed, 3 Apr 2019 16:14:52 +0200
> Tristan Kohl <tristan@iceity.de> wrote:
>
>> Hey guys,
>>
>> I build most of my images on top of Alpine. However for the last couple
>> of days I come accross some weird problem which causes apk add to hang
>> for some packages. I tried following Dockerfile on an Alpine 3.9 host
>> with Docker 18.09.1-ce and my Void Linux desktop with docker 18.09.4.
>>
>>
>> FROM alpine:latest
>>
>> RUN apk add --no-cache build-base cmake git linux-headers perl
>>
>> <snip>
>>
>>
>>
>> #> docker build -t test .  
>> Sending build context to Docker daemon   2.56kB
>> Step 1/18 : FROM alpine:latest
>>  ---> 5cb3aa00f899  
>> Step 2/18 : RUN apk add --no-cache build-base cmake git linux-headers perl
>>  ---> Running in 9736754a88cc  
>> fetch http://dl-cdn.alpinelinux.org/alpine/v3.9/main/x86_64/APKINDEX.tar.gz
>> fetch
>> http://dl-cdn.alpinelinux.org/alpine/v3.9/community/x86_64/APKINDEX.tar.gz
>> (1/41) Upgrading musl (1.1.20-r3 -> 1.1.20-r4)
>> (2/41) Installing binutils (2.31.1-r2)
>> (3/41) Installing libmagic (5.35-r0)
>> (4/41) Installing file (5.35-r0)
>> (5/41) Installing gmp (6.1.2-r1)
>> (6/41) Installing isl (0.18-r0)
>> (7/41) Installing libgomp (8.2.0-r2)
>> (8/41) Installing libatomic (8.2.0-r2)
>> (9/41) Installing libgcc (8.2.0-r2)
>> (10/41) Installing mpfr3 (3.1.5-r1)
>> (11/41) Installing mpc1 (1.0.3-r1)
>> (12/41) Installing libstdc++ (8.2.0-r2)
>> (13/41) Installing gcc (8.2.0-r2)
>>
>>
>> Process hangs here (I let it alone for >1h and then killed it), but
>> running an Alpine instance via
>>
>> docker run -it --rm alpine
>>
>> and trying to install those packages manually one by one has worked both
>> times I tried this (today and on Sunday). However, installing gcc or
>> build-base did not work (aka. hang) two or three times and only
>> succedded on consecutive tries. Weirdly enough, calling
>>
>> apk add g++
>>
>> pulled in gcc and finished within seconds as I was used to...
>>
>> So I "think" there is no problem with docker's network setup but I have
>> no idea of the inner workings so please tell me where to look if you
>> think this is a docker issue.
> This sounds like an MTU blackhole issue. I know that Fastly
> (dl-cdn.a.o) does not have a working PMTU, because they filter
> out need-to-frag ICMP packets. I guess its their DDoS feature that
> does.
>
> Check the MTU size in your container, on the host and in your LAN.
>
> If you host and container have differnet MTU size, then you can
> probably resolve it with clamp-mss on your host.
>
> There is also a tool called 'mtu' that can help you find where a
> blackhole is, in case it is a problem with your ISP or somewhere else
> on the internet.
>
>   apk add mtu
>
> -nc
>
>
>> Cheers,
>> Tristan
>>
>> P.S.: Previous builds ~2 weeks ago worked and there was no docker update
>> as far as I can remember.
>>
>>
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