Container building from chapter 3 throwing error.

[Ruhshan]

Here is the full command and output:

`➜ Chapter03 git:(master) docker build -f docker/app/Dockerfile --tag thoughts-backend .
[+] Building 3.8s (7/23)
=> [internal] load build definition from Dockerfile 0.0s
=> => transferring dockerfile: 37B 0.0s
=> [internal] load .dockerignore 0.0s
=> => transferring context: 2B 0.0s
=> [internal] load metadata for docker.io/library/alpine:3.9 2.8s
=> [internal] load build context 0.0s
=> => transferring context: 1.30kB 0.0s
=> CACHED [compile-image 1/10] FROM docker.io/library/alpine:3.9@sha256:414e0518bb9228d35e4cd5165567fb91d26c6a214e9c95899e1e056fcd349011 0.0s
=> ERROR [compile-image 2/10] RUN apk add --update python3 0.9s
=> ERROR [runtime-image 2/10] RUN apk add --update python3 curl libffi postgresql-libs 0.9s

[compile-image 2/10] RUN apk add --update python3:
#12 0.360 fetch http://dl-cdn.alpinelinux.org/alpine/v3.9/main/x86_64/APKINDEX.tar.gz
#12 0.544 fetch http://dl-cdn.alpinelinux.org/alpine/v3.9/community/x86_64/APKINDEX.tar.gz
#12 0.545 ERROR: http://dl-cdn.alpinelinux.org/alpine/v3.9/main: BAD signature
#12 0.545 WARNING: Ignoring APKINDEX.b89edf6e.tar.gz: No such file or directory
#12 0.839 ERROR: http://dl-cdn.alpinelinux.org/alpine/v3.9/community: BAD signature
#12 0.839 WARNING: Ignoring APKINDEX.737f7e01.tar.gz: No such file or directory
#12 0.840 ERROR: unsatisfiable constraints:
#12 0.841 python3 (missing):
#12 0.841 required by: world[python3]

---

---

[runtime-image 2/10] RUN apk add --update python3 curl libffi postgresql-libs:
#5 0.388 fetch http://dl-cdn.alpinelinux.org/alpine/v3.9/main/x86_64/APKINDEX.tar.gz
#5 0.535 ERROR: http://dl-cdn.alpinelinux.org/alpine/v3.9/main: BAD signature
#5 0.536 WARNING: Ignoring APKINDEX.b89edf6e.tar.gz: No such file or directory
#5 0.536 fetch http://dl-cdn.alpinelinux.org/alpine/v3.9/community/x86_64/APKINDEX.tar.gz
#5 0.833 ERROR: http://dl-cdn.alpinelinux.org/alpine/v3.9/community: BAD signature
#5 0.833 WARNING: Ignoring APKINDEX.737f7e01.tar.gz: No such file or directory
#5 0.833 ERROR: unsatisfiable constraints:
#5 0.836 curl (missing):
#5 0.836 required by: world[curl]
#5 0.836 libffi (missing):
#5 0.836 required by: world[libffi]
#5 0.836 postgresql-libs (missing):
#5 0.836 required by: world[postgresql-libs]
#5 0.836 python3 (missing):
#5 0.836 required by: world[python3]

---

executor failed running [/bin/sh -c apk add --update python3]: exit code: 1`

[jaimebuelta]

This seems to be a problem when downloading dependencies from Alpine

[runtime-image 2/10] RUN apk add --update python3 curl libffi postgresql-libs:
#5 0.388 fetch http://dl-cdn.alpinelinux.org/alpine/v3.9/main/x86_64/APKINDEX.tar.gz
#5 0.535 ERROR: http://dl-cdn.alpinelinux.org/alpine/v3.9/main: BAD signature
#5 0.536 WARNING: Ignoring APKINDEX.b89edf6e.tar.gz: No such file or directory
#5 0.536 fetch http://dl-cdn.alpinelinux.org/alpine/v3.9/community/x86_64/APKINDEX.tar.gz
#5 0.833 ERROR: http://dl-cdn.alpinelinux.org/alpine/v3.9/community: BAD signature
#5 0.833 WARNING: Ignoring APKINDEX.737f7e01.tar.gz: No such file or directory
#5 0.833 ERROR: unsatisfiable constraints:

I've seen this problem sometimes, and it's a transient problem. I tried the same command and it worked as expected. Can you please retry?