Team,

If we try to create index using misplaced background configuration, MongoDB should be able to validate and report back the error. For example, if I run following command, server doesn't tells me that background is placed wrong and instead runs the indexing in foreground:

db.runCommand({
	createIndexes: "exampleIndex",
	indexes: [{
		key: {
			a: 1,
			b: 1,
			"c": 1
		},
		name: "a_1_b_1_c_1"
	},
	{
		key: {
			a: 1,
			b: 1,
			c: 1,
			"d": 1,
			e: 1
		},
		name: "a_1_b_1_c_1_d_1_e_1"
	}]
},{ background: true })

Note that the background: true is not present per index level but is defined at global level.