ConstraintLayout margins

You should avoid using nested views inside ConstraintLayout. The reasons are:

• ConstraintLayout allows you to create large and complex layouts with a flat view hierarchy (no nested view groups) as it's stated in Build a Responsive UI with ConstraintLayout

• Traditional nested layout hierarchy negatively impacts on performance as it's stated in Understanding the performance benefits of ConstraintLayout

The result layout source should look like:

<android.support.constraint.ConstraintLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:background="@color/colorDarkGray">

    <TextView
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_centerVertical="true"
        android:alpha="0.7"
        android:fontFamily="sans-serif"
        android:letterSpacing="0.03"
        android:text="Another text"
        android:textColor="@color/colorWhite"
        android:textSize="11sp"
        android:textStyle="normal"
        android:id="@+id/textView"
        android:layout_marginTop="8dp"
        android:layout_marginLeft="8dp"
        android:layout_marginRight="8dp"
        android:layout_marginBottom="8dp"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toLeftOf="@+id/textView2"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintHorizontal_chainStyle="spread" />

    <TextView
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_alignParentRight="true"
        android:layout_centerVertical="true"
        android:gravity="end"
        android:fontFamily="sans-serif"
        android:letterSpacing="0.03"
        android:text="Some text"
        android:textColor="@color/colorWhite"
        android:textSize="11sp"
        android:textStyle="normal"
        android:id="@+id/textView2"
        android:layout_marginTop="8dp"
        android:layout_marginLeft="8dp"
        android:layout_marginRight="8dp"
        android:layout_marginBottom="8dp"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintLeft_toRightOf="@+id/textView"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintBottom_toBottomOf="parent" />

</android.support.constraint.ConstraintLayout>

You can learn how to build layouts with ConstraintLayouts by following steps in Google's Codelab.

Try this change your RelativeLayout width to android:layout_width="0dp"

<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:background="@color/colorDarkGray">


    <RelativeLayout
        android:id="@+id/container3"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_marginBottom="8dp"
        android:layout_marginStart="8dp"
        android:layout_marginLeft="8dp"
        android:layout_marginRight="8dp"
        android:layout_marginEnd="8dp"
        android:layout_marginTop="8dp"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintTop_toTopOf="parent">

        <TextView
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_centerVertical="true"
            android:alpha="0.7"
            android:fontFamily="sans-serif"
            android:letterSpacing="0.03"
            android:text="Another text"
            android:textColor="@color/colorWhite"
            android:textSize="11sp"
            android:textStyle="normal" />

        <TextView
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_alignParentRight="true"
            android:layout_centerVertical="true"
            android:fontFamily="sans-serif"
            android:letterSpacing="0.03"
            android:text="Some text"
            android:textColor="@color/colorWhite"
            android:textSize="11sp"
            android:textStyle="normal" />
    </RelativeLayout>
</android.support.constraint.ConstraintLayout>

Yes, of course there're no left and right margins in your layout when you're defining your RelativeLayout as below:

<RelativeLayout
    android:id="@+id/container3"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_marginBottom="8dp"
    android:layout_marginStart="8dp"
    android:layout_marginLeft="8dp"
    android:layout_marginRight="8dp"
    android:layout_marginEnd="8dp"
    android:layout_marginTop="8dp"
    app:layout_constraintBottom_toBottomOf="parent"
    app:layout_constraintStart_toStartOf="parent"
    app:layout_constraintEnd_toEndOf="parent"
    app:layout_constraintTop_toTopOf="parent"

That means RelativeLayout has wrap_content width and height and it's in the center of Parent (with our constraintTop,Bot....).

How to solve it? Just set the width of your relative layout to 0dp. According to constraints, that means your RelativeLayout will be as wide as parent.