Why i get permission denied at docker ffmpeg execution - docker

Question

i want to make small gifs (miniclip) from a mp4 video using ffmpeg with php script in aws ecs.
The whole configuration is working with the symfony built-in server. Now i put the controller into local docker and now i get the following permission denied error:
ffmpeg version 5.0.1 Copyright (c) 2000-2022 the FFmpeg developers built with gcc 11.2.1
(Alpine 11.2.1_git20220219) 20220219 configuration: --prefix=/usr --enable-avfilter --
enable-gnutls --enable-gpl --enable-libass --enable-libmp3lame --enable-libpulse --
enable-libvorbis --enable-libvpx --enable-libxvid --enable-libx264 --enable-libx265 --
enable-libtheora --enable-libv4l2 --enable-libdav1d --enable-lto --enable-postproc --
enable-pic --enable-pthreads --enable-shared --enable-libxcb --enable-librist --enable-
libsrt --enable-libssh --enable-libvidstab --disable-stripping --disable-static --
disable-librtmp --enable-libaom --enable-libopus --enable-libsoxr --enable-libwebp --
enable-vaapi --enable-vdpau --enable-vulkan --enable-libdrm --disable-debug
libavutil 57. 17.100 / 57. 17.100
libavcodec 59. 18.100 / 59. 18.100
libavformat 59. 16.100 / 59. 16.100
libavdevice 59. 4.100 / 59. 4.100
libavfilter 8. 24.100 / 8. 24.100
libswscale 6. 4.100 / 6. 4.100
libswresample 4. 3.100 / 4. 3.100
libpostproc 56. 3.100 / 56. 3.100
Input #0, mov,mp4,m4a,3gp,3g2,mj2,
from 'https://vendery-streaming.fra1.cdn.digitaloceanspaces.com/myvideo.mp4': Metadata: major_brand : isom minor_version : 512
compatible_brands: isomiso2avc1mp41
encoder : Lavf58.24.101 Duration: 00:18:10.37, start: 0.000000,
bitrate: 3405 kb/s Stream #0:0[0x1](und):
Video: h264 (High) (avc1 / 0x31637661), yuv420p(progressive), 540x960, 3331 kb/s, 30
fps, 30 tbr, 15360 tbn (default) Metadata: handler_name : VideoHandler vendor_id : [0][0][0][0]
Stream #0:1[0x2](und): Audio: aac (LC) (mp4a / 0x6134706D), 44100 Hz, mono,
fltp, 69 kb/s (default)
Metadata: handler_name :
SoundHandler vendor_id : [0][0][0][0] /var/www/html/public/myimage.gif: Permission denied
What exactly tells me the error? The folder /var/www/html/public/ exists but isnt writable?
The command from php i run the script is:
$output = shell_exec('/usr/bin/ffmpeg -y -ss 255 -t 4 -i '.$url.' -vf "fps=10,scale=320:-1:flags=lanczos,split[s0][s1];[s0]palettegen[p];[s1][p]paletteuse" -loop 0 /var/www/html/public/'.$outputFile.' 2>&1');
echo $output;
any idea is welcome.
the user is wrong. shell_exec('whoami'); gives me www-data, but why?? My dockerfile have the following in: RUN chown -R root:root /var/www/html/public
docker-compose.yaml
symfony:
mem_limit: 500M
mem_reservation: 500M
container_name: '${APP_NAME}-${APP_ENV}-backend'
#environment:
#- DATABASE_URL="mysql://${MYSQL_USER}:${MYSQL_PASS}#database/${MYSQL_DB}?serverVersion=mariadb-10.8.3"
build:
context: .
target: symfony
#restart: unless-stopped
ports:
- 8000:8000 #browser / container