Package Index: Build in Dockerhub (#13810)

* Package Index: Build in Dockerhub

Prepare to build the package index service, packages.spack.io,
on Dockerhub.

Local build (in spack root dir):
```
docker build -t spack/packages.spack.io:latest -f share/spack/docker/package-index/Dockerfile .
```

Local test:
```
docker run -p 8080:80 spack/packages.spack.io:latest
```

* Travis-CI: Remove Docker

Remove leftover docker stages from Travis-CI.

* Simplify Split Call

share/spack/docker/package-index/Dockerfile

@@ -0,0 +1,30 @@
+# prepare the package index in form of JSON files
+FROM ubuntu:18.04 AS build-env
+
+ENV SPACK_ROOT=/opt/spack             \
+    DEBIAN_FRONTEND=noninteractive
+
+COPY bin     $SPACK_ROOT/bin
+COPY etc     $SPACK_ROOT/etc
+COPY lib     $SPACK_ROOT/lib
+COPY share   $SPACK_ROOT/share
+COPY var     $SPACK_ROOT/var
+
+RUN apt-get -yqq update   \
+ && apt-get -yqq install  \
+        bash jq python    \
+ && rm -rf /var/lib/apt/lists/*
+
+WORKDIR /build
+# single, large index file
+RUN $SPACK_ROOT/bin/spack list --format version_json > packages.json
+# individual packages split into a tree of :firstLetter/:packageName.json
+RUN $SPACK_ROOT/share/spack/docker/package-index/split.sh
+
+# nginx web service
+FROM nginx:mainline-alpine
+MAINTAINER Spack Maintainers <maintainers@spack.io>
+COPY --from=build-env --chown=nginx:nginx /build/packages /build/packages.json /usr/share/nginx/html/api/
+COPY share/spack/docker/package-index/cors-header.conf /etc/nginx/conf.d/
+
+CMD ["nginx", "-g", "daemon off;"]

share/spack/docker/package-index/README.rst

@@ -0,0 +1,45 @@
+============================================
+The packages.spack.io Package Index REST API
+============================================
+
+This directory provides the docker recipe for the Spack package index on https://packages.spack.io
+
+On each merge to ``develop``, DockerHub builds a new image ``spack/packages.spack.io`` which is configured in:
+  https://cloud.docker.com/u/spack/repository/docker/spack/packages.spack.io/builds/edit
+
+------------
+The REST API
+------------
+
+The API is a simple, file-based JSON index.
+A specific package can be queried via the URI syntax:
+``https://packages.spack.io/api/:firstLetter/:packageName.json``
+which will return a HTTP status code ``200`` with a JSON file for all valid packages (content from ``spack list --format version_json``) and HTTP status code ``404`` for all other package names.
+
+Examples:
+
+- https://packages.spack.io/api/a/adios2.json
+- https://packages.spack.io/api/p/py-pandas.json
+
+There is also the full index available at once under https://packages.spack.io/api/packages.json
+
+Current down-stream dependencies are, e.g. the https://shields.io service:
+
+- https://shields.io/category/version
+- https://github.com/badges/shields/pull/3536
+
+--------------------
+Local Build and Test
+--------------------
+
+Execute in your local Spack source root directory:
+
+.. code-block:: bash
+
+   docker build -t spack/packages.spack.io:latest -f share/spack/docker/package-index/Dockerfile .
+
+Startup a local HTTP server on http://localhost:8080 via:
+
+.. code-block:: bash
+
+   docker run -p 8080:80 spack/packages.spack.io:latest

share/spack/docker/package-index/cors-header.conf

@@ -0,0 +1,3 @@
+# potentially add even more for preflight support
+# https://enable-cors.org/server_nginx.html
+add_header 'Access-Control-Allow-Origin' '*';

share/spack/docker/package-index/split.sh

@@ -0,0 +1,20 @@
+#!/usr/bin/env bash
+#
+# Copyright 2013-2019 Lawrence Livermore National Security, LLC and other
+# Spack Project Developers. See the top-level COPYRIGHT file for details.
+#
+# SPDX-License-Identifier: (Apache-2.0 OR MIT)
+
+# split the package index in a small file tree of
+#    /p/package.json
+# files with sub-directories grouped by the initial letter of the packages
+
+base_dir=$(pwd)/packages/
+
+for pkg in $(cat packages.json | jq -c '.[]')
+do
+    name="$(echo ${pkg} | jq -r '.name')";
+    first_letter=${name::1}
+    mkdir -p ${base_dir}${first_letter}/
+    echo ${pkg} > ${base_dir}${first_letter}/${name}.json
+done